• 11.14.2015
• etc

The go-to rebuttal to increasing automation tends to be something around how creativity could not be emulated by computers, at least, not for awhile. There's some truth to that statement depending on how you define "creativity", I suppose. The least charitable definition might be synonymous with "content generation", a domain typically exclusive to humans - artists, musicians, writers, and so on - but computers have made some claim to this territory.

The poster child of the automated (i.e. procedural) content generation beachhead is No Man's Sky, which generates a literal universe, complete with stars and beaches and creatures, using interweaving mathematical equations. The universe it generates will reportedly take 5 billion years to explore, and that's just one of those universes. In theory, an infinite amount of universes can be generated by setting different seed values (the value which is used to determine all other values in the game). This interview with Sean Murray goes a bit more into depth on their approach.

These procedurally-generated universes aren't random, though they are designed to give that appearance. They are completely deterministic depending on the seed value - this is a critical property since there needs to be consistency. If you leave a planet, you should not only be able to come back to that planet, but it should be in a similar state to when you left it.

A big challenge in procedural content generation is figuring out a way of creating things which feel organic and natural - for No Man's Sky, the solution is the impressive-sounding Superformula, developed by John Gielis in 2003. In polar coordinates, with radius $r$ and angle $\varphi$, parameterized by $a, b, m, n_1, n_2, n_3$, the Superformula is:

$$r\left(\varphi\right) = \left( \left| \frac{\cos\left(\frac{m\varphi}{4}\right)}{a} \right| ^{n_2} + \left| \frac{\sin\left(\frac{m\varphi}{4}\right)}{b} \right| ^{n_3} \right) ^{-\frac{1}{n_{1}}}.$$

The above is the formula for two dimensions, but it is easily generalized to higher dimensions as well by using spherical products of superformulas (cf. Wikipedia).

Some forms resulting from the 2D formula:

Procedural generation is a really beautiful approach to game design. It's not so much about creating a specific experience but rather about defining the conditions for limitless experiences. No Man's Land is far from the first to do this, but it is the first (as far as I know) to have all of its content procedurally generated. The game Elite (from 1984!) also had procedurally-generated universe. Elite's universe was much simpler of course, but used a clever approach using the Fibonacci sequence to simulate randomness:

\begin{aligned} x_0 &= \text{seed} \\ x_n &= x_{n-1} + x_{n-2} \end{aligned}

And then taking the last few digits of values generated from this sequence.

For example, take the Fibonacci sequence:

$$0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, \dots$$

Let's jump at head in the sequence:

$$1597, 2584, 4181, 6765, 10946, 17711, 28657, \dots$$

If we just look at the last three digits, the resulting sequence looks quite random:

$$597, 584, 181, 765, 946, 711, 657, \dots$$

Procedural content generation is interesting, but other games focus on "procedural" stories. These games have (some) manually generated content - creatures, buildings, etc - but focus on designing complex systems which form the bedrock of the game's ability to spawn wild and fantastic stories. Dwarf Fortress and RimWorld are two great examples, which are essentially fantasy and sci-fi world-simulators (respectively) which model things like each individual's mental health, weather patterns, crop growth, and so on. No one writes the stories ahead of time, no one has a premeditated experience for you put in place - it's all off-the-cuff based on the dynamics of the game's rules.

The stories that come out of these games are amazing. Dwarf Fortress has an especially vibrant community based around the often absurd things that happen in game (for example, see r/dwarffortress, or for a more academic treatment, see Josh Diaz's thesis).

With the independent game industry continually expanding, I think we'll see more of these kinds of games. They can be developed with relatively small teams but have the richness and depth (and often to a better degree) of a massively-built studio game.

# coral metrics sketch

• 11.12.2015
• etc

As part of the Coral Project, we're trying to come up with some interesting and useful metrics about community members and discussion on news sites.

It's an interesting exercise to develop metrics which embody an organization's principles. For instance - perhaps we see our content as the catalyst for conversations, so we'd measure an article's success by how much discussion it generates.

Generally, there are two groups of metrics that I have been focusing on:

• Asset-level metrics, computed for individual articles or whatever else may be commented on
• User-level metrics, computed for individual users

For the past couple of weeks I've been sketching out a few ideas for these metrics:

• For assets, the principles that these metrics aspire to capture are around quantity and diversity of discussion.
• For users, I look at organizational approval, community approval, how much discussion this user tends to generate, and how likely they are to be moderated.

Here I'll walk through my thought process for these initial ideas.

## Asset-level metrics

For assets, I wanted to value not only the amount of discussion generated but also the diversity discussions. A good discussion is one in which there's a lot of high-quality exchange (something else to be measured, but not captured in this first iteration) from many different people.

There are two scores to start:

• a discussion score, which quantifies how much discussion an asset generated. This looks at how much people are talking to each other as opposed to just counting up the number of comments. For instance, a comments section in which all comments are top-level should not have a high discussion score. A comments section in which there are some really deep back-and-forths should have a higher discussion score.
• a diversity score, which quantifies how many different people are involved in the discussions. Again, we don't want to look at diversity in the comments section as a whole because we are looking for diversity within discussions, i.e. within threads.

The current sketch for computing the discussion score is via two values:

• maximum thread width: what is the highest number of replies for a comment?

These are pretty rough approximations of "how much discussion" there is. The idea is that for sites which only allow one level of replies, a lot of replies to a comment can signal a discussion, and that a very deep thread signals the same for sites which allow more nesting.

The discussion score of a top-level thread is the product of these two intermediary metrics:

$$\text{discussion score}_{\text{thread}} = \max(\text{thread}_{\text{depth}}) \max(\text{thread}_{\text{width}})$$

The discussion score for the entire asset is the value that answers this question: if a new thread were to start in this asset, what discussion score would it have?

The idea is that if a section is generating a lot of discussion, a new thread would likely also involve a lot of discussion.

The nice thing about this approach (which is similar to the one used throughout all these sketches) is that we can capture uncertainty. When a new article is posted, we have no idea how good of a discussion a new thread might be. When we have one or two threads - maybe one is long and one is short - we're still not too sure, so we still have a fairly conservative score. But as more and more people comment, we begin to narrow down on the "true" score for the article.

More concretely (skip ahead to be spared of the gory details), we assume that this discussion score is drawn from a Poisson distribution. This makes things a bit easier to model because we can use the gamma distribution as a conjugate prior.

By default, the gamma prior is parameterized with $k=1, \theta=2$ since it is a fairly conservative estimate to start. That is, we begin with the assumption that any new thread is unlikely to generate a lot of discussion, so it will take a lot of discussion to really convince us otherwise.

Since this gamma-Poisson model will be reused elsewhere, it is defined as its own function:

def gamma_poission_model(X, n, k, theta, quantile):
k = np.sum(X) + k
t = theta/(theta*n + 1)
return stats.gamma.ppf(quantile, k, scale=t)


Since the gamma is a conjugate prior here, the posterior is also a gamma distribution with easily-computed parameters based on the observed data (i.e. the "actual" top-level threads in the discussion).

We need an actual value to work with, however, so we need some point estimate of the expected discussion score. However, we don't want to go with the mean since that may be too optimistic a value, especially if we only have a couple top-level threads to look at. So instead, we look at the lower-bound of the 90% credible interval (the 0.05 quantile) to make a more conservative estimate.

So the final function for computing an asset's discussion score is:

def asset_discussion_score(threads, k=1, theta=2):
n = len(X)

k = np.sum(X) + k
t = theta/(theta*n + 1)

return {'discussion_score': gamma_poission_model(X, n, k, theta, 0.05)}


A similar approach is used for an asset's diversity score. Here we ask the question: if a new comment is posted, how likely is it to be a posted by someone new to the discussion?

We can model this with a beta-binomial model; again, the beta distribution is a conjugate prior for the binomial distribution, so we can compute the posterior's parameters very easily:

def beta_binomial_model(y, n, alpha, beta, quantile):
alpha_ = y + alpha
beta_ = n - y + beta
return stats.beta.ppf(quantile, alpha_, beta_)


Again we start with conservative parameters for the prior, $\alpha=2, \beta=2$, and then compute using threads as evidence:

def asset_diversity_score(threads, alpha=2, beta=2):
X = set()
n = 0
X = X | users
y = len(X)

return {'diversity_score': beta_binomial_model(y, n, alpha, beta, 0.05)}


Then averages for these scores are computed across the entire sample of assets in order to give some context as to what good and bad scores are.

## User-level metrics

User-level metrics are computed in a similar fashion. For each user, four metrics are computed:

• a community score, which quantifies how much the community approves of them. This is computed by trying to predict the number of likes a new post by this user will get.
• an organization score, which quantifies how much the organization approves of them. This is the probability that a post by this user will get "editor's pick" or some equivalent (in the case of Reddit, "gilded", which isn't "organizational" but holds a similar revered status).
• a discussion score, which quantifies how much discussion this user tends to generate. This answers the question: if this user starts a new thread, how many replies do we expect it to have?
• a moderation probability, which is the probability that a post by this user will be moderated.

The community score and discussion score are both modeled as gamma-Poission models using the same function as above. The organization score and moderation probability are both modeled as beta-binomial models using the same function as above.

## Time for more refinement

These metrics are just a few starting points to shape into more sophisticated and nuanced scoring systems. There are some desirable properties missing, and of course, every organization has different principles and values, and so the ideas presented here are not one-size-fits-all, by any means. The challenge is to create some more general framework that allows people to easily define these metrics according to what they value.

# Machine Learning 101

• 11.10.2015
• etc

This post is an adaptation from a talk given at artsec and a workshop given at a few other places (Buenos Aires Media Party 2015, MozFest 2015). The goal is to provide an intuition on machine learning for people without advanced math backgrounds - given that machine learning increasingly rules everything around us, everyone should probably have some mental model of how it works.

The materials for the workshop are available on GitHub.

## What is "machine learning" anyways?

There are plenty of introductory machine learning tutorials and courses available, but they tend to focus on cursory tours of algorithms - here's linear regression, here's SVMs, here's neural networks, etc - without building an intuition of what machine learning is actually doing under the hood. This intuition is obvious to practitioners but not for people new to the field. To get the full value of the other machine learning resources out there, that intuition really helps.

But first, to clarify a bit what machine learning is: a basic working definition could be "algorithms for computers to learn patterns". Pattern recognition is something that people are very good at, but difficult for computers to do.

Here we'll go through walkthrough a very simple machine learning task which is prototypical of many real-world machine learning problems. First we'll go through it by hand, noting where our human superpower of pattern recognition comes into play, and then think about how we can translate what we did into something a computer is capable of executing.

## Learning functions by hand

A common machine learning goal is to take a dataset and learn the pattern (i.e. relationship) between different variables of the data. Then that pattern can be used to predict values of those variables for new data.

Consider the following data:

If I were to ask you to describe the data by a pattern you see in that data, you'd likely draw a line. It is quite obvious to us that, even though the data points don't fall exactly in a line, a line seems to satisfactorily represent the data's pattern.

But a drawn line is no good - what are we supposed to do with it? It's hard to make use of that in a program.

A better way of describing a pattern is as a mathematical equation (i.e. a function). In this form, we can easily plug in new inputs to get predicted outputs. So we can restate our goal of learning a pattern as learning a function.

You may remember that lines are typically expressed in the form:

$$y = mx + b$$

As a refresher: $y$ is the output, $x$ is the input, $m$ is the slope, and $b$ is the intercept.

Lines are uniquely identified by values of $m$ and $b$:

Variables like $m$ and $b$ which unique identify a function are called parameters (we also say that $m$ and $b$ paramterize the line). So finding a particular line means finding particular values of $m$ and $b$. So when we say we want to learn a function, we are really saying that we want to learn the parameters of a function, since they effectively define the function.

So how can we find the right values of $m, b$ for the line that fits our data?

Trial-and-error seems like a reasonable approach. Let's start with $m=12, b=2$ (these values were picked arbitrarily, you could start with different values too). Trying $m=12, b=2$

The line is still quite far from the data, so let's try lowering the slope to $m=8$. Trying $m=8, b=2$

The line's closer, but still far from the data, so we can try lowering the slope again. Then we can check the resulting line, and continue adjusting until we feel satisfied with the result. Let's say we carry out this trial-and-error and end up with $m=4.6, b=40$. Trying $m=4.6, b=40$

So now we have a function, $y = 4.6x + b$, and if we got new inputs we could predict outputs that would follow the pattern of this dataset.

But this was quite a laborious process. Can we get a computer to do this for us?

## Learning functions by computer

The basic approach we took by hand was just to:

1. Pick some random values for $m$ and $b$
2. Compare the resulting line to the data to see if it's a good fit
3. Go back to 1 if the resulting line is not a good fit

This is a fairly repetitive process and so it seems like a good candidate for a computer program. There's one snag though - we could easily eyeball whether or not a line was a "good" fit. A computer can't eyeball a line like that.

So we have to get a bit more explicit about what a "good" fit is, in terms that a computer can make use of. To put it another way, we want the computer to be able to calculate how "wrong" its current guesses for $m$ and $b$ are. We can define a function to do so.

Let's think for a moment about what we would consider a bad-fitting line. The further the line was from the dataset, the worse we consider it. So we want lines that are close to our datapoints. We can restate this in more concrete terms.

First, let's notate our line function guess as $f(x)$. Each datapoint we have is represented as $(x, y)$, where $x$ is the input and $y$ is the output. For a datapoint $(x, y)$, we predict an output $\hat y$ based on our line function, i.e. $\hat y = f(x)$.

We can look at each datapoint and calculate how far it is from our line guess with $y - \hat y$. Then we can combine all these distances (which are called errors) in some way to get a final "wrongness" value.

There are many ways we can do this, but a common way is to square all of these errors (only the magnitude of the error is important) and then take their mean:

$$\frac{\sum (y - \hat y)^2 }{n}$$

Where $n$ is the number of datapoints we have.

$$\frac{\sum (y - f(x))^2 }{n}$$

To make it a bit clearer that the important part here is our guess at the function $f(x)$.

A function like this which calculates the "wrongness" of our current line guess is called a loss function (or a cost function). Clearly, we want to find a line (that is, values of $m$ and $b$) which are the "least wrong".

Another way of saying this is that we want to find parameters which minimize this loss function. This is basically what we're doing when we eyeball a "good" line.

When we guessed the line by hand, we just iteratively tried different $m$ and $b$ values until it looked good enough. We could use a similar approach with a computer, but when we did it, we again could eyeball how we should change $m$ and $b$ to get closer (e.g. if the line is going above the datapoints, we know we need to lower $b$ or lower $m$ or both). How then can a computer know in which direction to change $m$ and/or $b$?

Changing $m$ and $b$ to get a line that is closer to the data is the same as changing $m$ and $b$ to lower the loss. It's just a matter of having the computer figure out in what direction changes to $m$ and/or $b$ will lower the loss.

Remember that a derivative of a function tells us the rate of change at a specific point in that function. We could compute the derivative of the loss function with respect to our current guesses for $m$ and $b$. This will inform us as to which direction(s) we need to move in order to lower the loss, and gives us new guesses for $m$ and $b$.

Then it's just a matter of repeating this procedure - with our new guesses for $m$ and $b$, use the derivative of the loss function to figure out what direction(s) to move in and get new guesses, and so on.

To summarize, we took our trial-and-error-by-hand approach and turned it into the following computer-suited approach:

1. Pick some random values for $m$ and $b$
2. Use a loss function to compare our guess $f(x)$ to the data
3. Determine how to change $m$ and $b$ by computing the derivative of the loss function with respect to $f(x)$
4. Go back to 1 and repeat until the loss function can't get any lower (or until it's low enough for our purposes)

A lot of machine learning is just different takes on this basic procedure. If it had to be summarized in one sentence: an algorithm learns some function by figuring out parameters which minimize some loss function.

Different problems and methods involve variations on these pieces - different loss functions, different ways of changing the parameters, etc - or include additional flourishes to help get around the problems that can crop up.

## Beyond lines

Here we worked with lines, i.e. functions of the form $y = mx + b$, but not all data fits neatly onto lines. The good news is that this general approach applies to sundry functions, both linear and nonlinear. For example, neural networks can approximate any function, from lines to really crazy-looking and complicated functions.

To be honest, there is quite a bit more to machine learning than just this - figuring out how to best represent data is another major concern, for example. But hopefully this intuition will help provide some direction in a field which can feel like a disconnected parade of algorithms.

# Automatically identifying voicemails

• 09.21.2015
• etc

Back in 2015, prosecutor Alberto Nisman was found dead under suspicious circumstances, just as he was about to bring a complaint accusing the Argentinian President Fernández over interfering with investigations into the AMIA bombing that took place in 1994 (This Guardian piece provides some good background).

There were some 40,000 phone calls related to the case that La Nación was interested in exploring further. Naturally, that is quite a big number and it's hard to gather the resources to comb through that many hours of audio.

La Nación crowdsourced the labeling of about 20,000 of these calls into those that were interesting and those that were not (e.g. voicemails or bits of idle chatter). For this process they used CrowData, a platform built by Manuel Aristarán and Gabriela Rodriguez, two former Knight-Mozilla Fellows at La Nación. This left about 20,000 unlabeled calls.

While Juan and I were in Buenos Aires for the Buenos Aires Media Party and our OpenNews fellows gathering, we took a shot at automatically labeling these calls.

## Data preprocessing

The original data we had was in the form of mp3s and png images produced from the mp3s. wav files are easier to work with so we used ffmpeg to convert the mp3s. With wav files, it is just a matter of using scipy to load them as numpy arrays.

For instance:

import scipy.io import wavfile

print(data)
# [15,2,5,6,170,162,551,8487,1247,15827,...]


In the end however, we used librosa, which normalizes the amplitudes and computes a sample rate for the wav file, making the data easier to work with.

import librosa

print(data)
# [0.1,0.3,0.46,0.89,...]


These arrays can be very large depending on the audio file's sample rate, and quite noisy too, especially when trying to identify silences. There may be short spikes in amplitude in an otherwise "silent" section, and in general, there is no true silence. Most silences are just low amplitude but not exactly 0.

In the example below you can see that what a person might consider silence has a few bits of very quiet sound scattered throughout.

There is also "noise" in the non-silent parts; that is, the signal can fluctuate quite suddenly, which can make analysis unwieldy.

To address these concerns, our preprocessing mostly consisted of:

• Reducing the sample rate a bit so the arrays weren't so large, since the features we looked at don't need the precision of a higher sample rate.
• Applying a smoothing function to deal with intermittent spikes in amplitude.
• Zeroing out any amplitudes below 0.015 (i.e. we considered any amplitude under 0.015 to be silence).

Since we had about 20,000 labeled examples to process, we used joblib to parallelize the process, which improved speeds considerably.

## Feature engineering

Typically, the main challenge in a machine learning problem is that of feature engineering - how do we take the raw audio data and represent it in a way that best suits the learning algorithm?

Audio files can be easily visualized, so our approach benefited from our own visual systems - we looked at a few examples from the voicemail and non-voicemail groups to see if any patterns jumped out immediately. Perhaps the clearest two patterns were the rings and the silence:

• A voicemail file will also have a greater proportion of silence than sound. For this, we looked at the images generated from the audio and calculated the percentage of white pixels (representing silence) in the image.
• A voicemail file will have several distinct rings, and the end of the file comes soon after the last ring. The intuition here is that no one picks up during a voicemail - hence many rings - and no one stays on the line much longer after the phone stops ringing. So we consider both the number of rings and the time from the last ring to the end of the file.

### Ring analysis

Identifying the rings is a challenge in itself - we developed a few heuristics which seem to work fairly well. You can see our complete analysis here, but the general idea is that we:

• Identify non-silent parts, separated by silences
• Check the length of the silence that precedes the non-silent part, if it is too short or too long, it is not a ring
• Check the difference between maximum and minimum amplitudes of the non-silent part; it should be small if it's a ring

The example below shows the original audio waveform in green and the smoothed one in red. You can see that the rings are preceded by silences of a roughly equivalent length and that they look more like plateaus (flat-ish on the top). Another way of saying this is that rings have low variance in their amplitude. In contrast, the non-ring signal towards the end has much sharper peaks and vary a lot more in amplitude.

### Other features

We also considered a few other features:

• Variance: voicemails have greater variance, since there is lots of silence punctuated by high-amplitude rings and not much in between.
• Length: voicemails tend to be shorter since people hang up after a few rings.
• Max amplitude: under the assumption that human speech is louder than the rings
• Mean silence length: under the assumption that when people talk, there are only short silences (if any)

However, after some experimentation, the proportion of silence and the ring-based features performed the best.

## Selecting, training, and evaluating the model

With the features in hand, the rest of the task is straightforward: it is a simple binary classification problem. An audio file is either a voicemail or not. We had several models to choose from; we tried logistic regression, random forest, and support vector machines since they are well-worn approaches that tend to perform well.

We first scaled the training data and then the testing data in the same way and computed cross validation scores for each model:

LogisticRegression
roc_auc: 0.96 (+/- 0.02)
average_precision: 0.94 (+/- 0.03)
recall: 0.90 (+/- 0.04)
f1: 0.88 (+/- 0.03)
RandomForestClassifier
roc_auc: 0.96 (+/- 0.02)
average_precision: 0.95 (+/- 0.02)
recall: 0.89 (+/- 0.04)
f1: 0.90 (+/- 0.03)
SVC
roc_auc: 0.96 (+/- 0.02)
average_precision: 0.94 (+/- 0.03)
recall: 0.91 (+/- 0.04)
f1: 0.90 (+/- 0.02)


We were curious what features were good predictors, so we looked at the relative importances of the features for both logistic regression:

[('length', -3.814302896584862),
('last_ring_to_end', 0.0056240364270560934),
('percent_silence', -0.67390678402142834),
('ring_count', 0.48483923341906693),
('white_proportion', 2.3131580570928114)]


And for the random forest classifier:

[('length', 0.30593363755717351),
('last_ring_to_end', 0.33353202776482688),
('percent_silence', 0.15206534339705702),
('ring_count', 0.0086084243372190443),
('white_proportion', 0.19986056694372359)]


Each of the models perform about the same, so we combined them all with a bagging approach (though in the notebook above we forgot to train each model on a different training subset, which may have helped performance), where we selected the label with the majority vote from the models.

## Classification

We tried two variations on classifying the audio files, differing in where we set the probability cutoff for classifying a file as uninteresting or not.

in the balanced classification, we set the probability threshold to 0.5, so any audio file that has ≥ 0.5 of being uninteresting is classified as uninteresting. This approach labeled 8,069 files as discardable.
in the unbalanced classification, we set the threshold to the much stricter 0.9, so an audio file must have ≥ 0.9 chance of being uninteresting to be discarded. This approach labeled 5,785 files as discardable.

## Validation

We have also created a validation Jupyter notebook where we can cherry pick random results from our classified test set and verify the correctness ourselves by listening to the audio file and viewing its image.

The validation code is available here.

## Summary

Even though using machine learning to classify audio is noisy and far from perfect, it can be useful making a problem more manageable. In our case, our solution narrowed the pool of audio files to only those that seem to be more interesting, reducing the time and resources needed to find the good stuff. We could always double check some of the discarded ones if there’s time to do that.

# broca

• 07.31.2015
• etc

At this year's OpenNews Code Convening, Alex Spangher of the New York Times and I worked on broca, which is a Python library for rapidly experimenting with new NLP approaches.

Conventional NLP methods - bag-of-words vector space representations of documents, for example - generally work well, but sometimes not well enough, or worse yet, not well at all. At that point, you might want to try out a lot of different methods that aren't available in popular NLP libraries.

Prior to the Code Convening, broca was little more than a hodgepodge of algorithms I'd implemented for various projects. During the Convening, we restructured the library, added some examples and tests, and implemented in the key piece of broca: pipelines.

## Pipelines

The core of broca is organized around pipes, which take some input and produce some output, which are then chained into pipelines.

Pipes represent different stages of an NLP process - for instance, your first stage may involve preprocessing or cleaning up the document, the next may be vectorizing it, and so on.

In broca, this would look like:

from broca.pipeline import Pipeline
from broca.preprocess import Cleaner
from broca.vectorize import BoW

docs = [
# ...
# some string documents
# ...
]

pipeline = Pipeline(
Cleaner(),
BoW()
)

vectors = pipeline(docs)


Since a key part of broca is rapid prototyping, it makes it very easy to simultaneously try different pipelines which may vary in only a few components:

from broca.vectorize import DCS

pipeline = Pipeline(
Cleaner(),
[BoW(), DCS()]
)


This would produce a multi-pipeline consisting of two pipelines: one which vectorizes using BoW, the other using DCS.

Multi-pipelines often have shared components. In the example above, Cleaner() is in both pipelines. To avoid redundant processing, a key part of broca's pipelines is that the output for each pipe is "frozen" to disk.

These frozen outputs are identified by a hash derived from the input data and other factors. If frozen output exists for a pipe and its input, that frozen output is "defrosted" and returned, saving unnecessary processing time.

This way, you can tweak different components of the pipeline without worrying about needing to re-compute a lot of data. Only the parts that have changed will be re-computed.

## Included pipes

broca includes a few pipes:

• broca.tokenize includes various tokenization methods, using lemmas and a few different keyword extractors.
• broca.vectorize includes a traditional bag-of-words vectorizer, an implementation of "dismabiguated core semantics", and Doc2Vec.
• broca.preprocess includes common preprocessors - cleaning punctuation, HTML, and a few others.

## Other tools

Not everything in broca is a pipe. Also included are:

• broca.similarity includes similarity methods for terms and documents.
• broca.distance includes string distance methods (this may be renamed later).
• broca.knowledge includes some tools for dealing with external knowledge sources (e.g. other corpora or Wikipedia).

Though at some point these may also become pipes.

We made it really easy to implement your own pipes. Just inherit from the Pipe class, specify the class's input and output types, and implement the __call__ method (that's what's called for each pipe).

For example:

from broca.pipeline import Pipe

class MyPipe(Pipe):
input = Pipe.type.docs
output = Pipe.type.vecs

def __init__(self, some_param):
self.some_param = some_param

def __call__(self, docs):
# do something with docs to get vectors
vecs = make_vecs_func(docs, self.some_param)
return vecs


We hope that others will implement their own pipes and submit them as pull requests - it would be great if broca becomes a repository of sundry NLP methods which makes it super easy to quickly try a battery of techniques on a problem.

broca is available on GitHub and also via pip:

pip install broca