A Field Guide to Character Encodings

I recently gave a talk at PyCascades (a regional Python language conference) on character encodings and I thought it would be nice to put together a little primer on a couple different important character encodings.

wood-cube-abc-cube-letters-48898.jpeg

So many characters, so little time.

If you’re unfamiliar with character encodings, they’re just a variety of different systems used to map a string of binary (i.e. 1’s and 0’s) to a specific character. So the Euro character, €, would be represented as “111000101000001010101100” in a character encoding called UTF-8  but “10100100” in the Latin 9 encoding. There are a lot of different character encodings out there, so I’m just going to cover a handful that I think are especially interesting/important. 


  • Name: ASCII
  • Created: 1960
  • Also known as: American Standard Code for Information Interchange, US-ASCII
  • Most often seen: In legacy systems, especially U.S. government databases that need to be backward compatible

ASCII was the first widely-used character encoding. It has space for only 128 characters, and is best suited for English-language data.


  • Name: ISO 8859-1
  • Created: 1985
  • Also known as: Latin 1, code page 819, iso-ir-100, csISOLatin1, latin1, l1, IBM819, WE8ISO8859P1
  • Most often seen: Representing languages not covered by ASCII (like Spanish and Portuguese).

Latin 1 is the most popular of a large set of character encodings developed by the ISO (International Organization for Standardization) to deal with the fact that ASCII only really works well for English by adding additional characters. They did this by adding one extra bit to each character (8 instead of the 7 ASCII uses) so that they had space for 256 characters per encoding. However, since there are a lot of characters out there, there are 16 different ISO encodings that can handle different alphabets. (For example, ISO 8859-5 handles Cyrillic characters, while ISO 8859-11 maps Thai characters.)


  • Name: Windows-1252
  • Created: 1985
  • Also known as: CP-1252,  Latin 1/ISO 8859-1 (which it isn’t!), ANSI, ansinew
  • Most often seen: Mislabelled as Latin 1.

While the ISO was developing a standard set of character encodings, pretty much every large software company was also developing thier own set of proprietary encodings that did pretty much the same thing. Windows-1252 is slightly tweaked version of Latin 1, but Windows also had a bunch of different encodings, as did Apple, as did IBM. The 1980’s were a wild time for character encodings!


  • Name: Shift-JIS
  • Created: 1997
  • Also known as: Shift Japanese Industrial Standards, SJIS, Shift_JIS
  • Most often seen: For Japanese

So one thing you may notice about the character encodings above is that they’re all fairly small, i.e. can’t handle more than 256 characters. But what about a language that has way more than 256 characters, like Japanese? (Japanese has a phonetic writing system with 71 characters, as well as 85,000 kanji characters which each represent a single word.) Well, one solution is to create a different character encoding system specifically for that language with enough space for all the characters you’re going to want to use frequently. But, like with the ASCII-based encodings I talked about above, just one encoding isn’t quite enough to cover all the needs of the language, so a lot of variants and extensions popped up.


  • Name: UTF-8
  • Created: 1992
  • Also known as: Unicode Transformation Format – 8-bit
  • Most often seen: Pretty much everywhere, including >90% of text on the web. (That’s a good thing!)

Which brings us to UTF-8, the current standard for text encoding. The UTF encodings map from binary to what are known as Unicode codepoints, and then those codepoints are mapped to characters. Why the whole “codepoints” thing in the middle? To help overcome the problems with language-specific encodings that were discussed above. There are over one million codepoints, of which a little over 130,000 have actually been assigned to specific characters. You can update which binary patterns map to which codepoints independently of which codepoints map to which characters. The large number of code points also means that UTF encodings are also pretty future-proof: we have space to add a lot of new characters before we run out. And, in case you’re wondering, there is a single body in charge of determining which code points map to which characters (including emoji!). It’s called the Unicode Consortium and anyone’s free to join.


Like I mentioned, there are lots of different character encodings out there, but knowing about these five and how they’re related will give you a good idea of the complexities of the character encodings landscape. If you’re curious to learn more, the Unicode Standard is a good place to start.

 

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How to be wrong: Measuring error in machine learning models

One thing I remember very clearly from writing my dissertation is how confused I initially was about which particular methods I could use to evaluate how often my models were correct or wrong. (A big part of my research was comparing human errors with errors from various machine learning models.) With that in mind, I thought it might be handy to put together a very quick equation-free primer of some different ways of measuring error.

The first step is to figure out what type of model you’re evaluating. Which type of error measurement you use depends on the type of model you’re evaluating. This was a big part of what initially confused me: much of my previous work had been with regression, especially mixed-effects regression, but my dissertation focused on multi-class classification instead. As a result, the techniques I was used to using to evaluate models just didn’t apply.

Today I’m going to talk about three types of models: regression, binary classification and multiclass classification.

Regression

In regression, your goal is to predict the value of an output value given one or more input values. So you might use regression to predict how much a puppy will weigh in four months or the price of cabbage. (If you want to learn more about regression, I recently put together a beginner’s guide to regression with five days of exercises.)

  • R-squared: This is a measurement of how correlated your predicted values are with the actual observed values. It ranges from 0 to 1, with 0 being no correlation and 1 being perfect correlation. In general, models with higher r-squareds are a better fit for your data.
  • Root mean squared error (RMSE), aka standard error: This measurement is an average of how wrong you were for each point you predicted. It ranges from 0 up, with closer to zero being better. Outliers (points you were really wrong about) will disproportionately inflate this measure.

Binary Classification

In binary classification, you aim to predict which of two classes an observation will fall. Examples include predicting whether a student will pass or fail a class or whether or not a specific passenger survived on the Titanic. This is a very popular type of model and there are a lot of ways of evaluating them, so I’m just going to stick to the four that I see most often in the literature.

  • Accuracy: This is proportion of the test cases that your model got right. It ranges from 0 (you got them all wrong) to 1 (you got them all right).
  • Precision: This is a measure of how good your model is at selecting only the members of a certain class. So if you were predicting whether students would pass or not and all of the students you predicted would pass actually did, then your model would have perfect precision. Precision ranges from 0 (none of the observations you said were in a specific class actually were) to 1 (all of the observations you said were in that class actually were). It doesn’t tell you about how good your model is at identifying all the members of that class, though!
  • Recall (aka True Positive Rate, Specificity): This is a measure of how good your model was at finding all the data points that belonged to a specific class. It ranges from 0 (you didn’t find any of them) to 1 (you found all of them). In our students example, a model that just predicted all students would pass would have perfect recall–since it would find all the passing students–but probably wouldn’t have very good precision unless very few students failed.
  • F1 (aka F-Score): The F score is the (harmonic) mean of both precision and recall. It also ranges from 0 to 1. Like precision and recall, it’s calculated based on a specific class you’re interested in. One thing to note about precision, recall and F1 is that they all don’t count true negatives (when you guessed something wasn’t in a specific class and you were right) so if that’s an important consideration for your model you probably shouldn’t rely on these measures.

Multiclass Classification

Multiclass classification is the task of determining which of three or more classes a specific observation belongs to. Things like predicting which icecream flavor someone will buy or automatically identifying the breed of a dog are multiclass classification.

  • Confusion Matrix: One of the most common ways to evaluate multiclass classifications is with a confusion matrix, which is a table with the actual labels along one axis and the predicted labels along the other (in the same order). Each cell of the table has a count value for the number of predictions that fell into that category. Correct predictions will fall along the center diagonal. This won’t give you a single summary measure of a system, but it will let you quickly compare performance across different classes.
  • Cohen’s Kappa: Cohen’s kappa is a measure of how much better than chance a model is at assigning the correct class to an observation. It range from -1 to 1, with higher being better. 0 indicates that the model is at chance levels (i.e. you could do as well just by randomly guessing). (Note that there are some people who will strongly advise against using Cohen’s Kappa.)
  • Informedness (aka Powers’ Kappa): Informedness tells us how likely we are to make an informed decision rather than a random guess. It is the true positive rate (aka recall) plus the true negative rate, minus 1. Like precision, recall and F1, it’s calculated on a class-by-class basis but we can calculate it for a multiclass classification model by taking the (geometric) mean across all of the classes. It ranges from -1 to 1, with 1 being a model that always makes correct predictions, 0 being a model that makes predictions that are no different than random guesses and -1 being a model that always makes incorrect predictions.

Packages for analysis

For R, the Metrics package and caret package both have implementations of these model metrics, and you’ll often find functions for evaluating more specialized models in the packages that contain the models themselves. In Python, you can find implementations of many of these measurements in the scikit-learn module.

Also, it’s worth noting that any single-value metric can only tell you part of the story about a model. It’s important to consider things besides just accuracy when selecting or training the best model for your needs.

Got other tips and tricks for measuring model error? Did I leave out one of your faves? Feel free to share in the comments. 🙂

Analyzing Multilingual Data

This blog post is a little different from my usual stuff. It’s based on a talk I gave yesterday at the first annual Data Institute Conference. As a result, it’s aimed at a slightly more technical audience than my usual stuff, but I hope I’ve done an ok job keeping it accessible. Feel free to drop me a comment if you have any questions or found anything confusing and I’ll be sure to help you out.
You can play with the code yourself by forking this notebook on Kaggle (you don’t even have to download or install anything :).

There are over 7000 languages in the world, 80% of which have fewer than a million speakers each. In fact, six in ten people on Earth speak a language with less than ten million speakers. In other words: the majority of people on Earth use low-resource languages.

As a result, any large sample of user-generated text is almost guaranteed to have multiple languages in it. So what can you do about it? There are a couple options:

  1. Ignore it
  2. Only look at the parts of the data that are in English
  3. Break the data apart by language & use language-specific tools when available

Let’s take a quick look at the benefits and drawbacks of each approach.


Getting started

In [1]:
# import libraries we'll use
import spacy # fast NLP
import pandas as pd # dataframes
import langid # language identification (i.e. what language is this?)
from nltk.classify.textcat import TextCat # language identification from NLTK
from matplotlib.pyplot import plot # not as good as ggplot in R :p

To explore working with multilingual data, let’s look a real-life dataset of user-generated text. This dataset contains 10,502 tweets, randomly sampled from all publicly available geotagged Twitter messages. It’s a realistic cross-section of the type of linguistic diversity you’ll see in a large text dataset.

# read in our data
tweetsData = pd.read_csv("../input/all_annotated.tsv", sep = "\t")

# check out some of our tweets
tweetsData['Tweet'][0:5]
0                            Bugün bulusmami lazimdiii
1       Volkan konak adami tribe sokar yemin ederim :D
2                                                  Bed
3    I felt my first flash of violence at some fool...
4              Ladies drink and get in free till 10:30
Name: Tweet, dtype: object

Option 1: Ignore the multilingualism

Maybe you’ve got a deadline coming up fast, or maybe you didn’t get a chance to actually look at some of your text data and just decide to treat it as if it were English. What could go wrong?

To find out, let’s use Spacy to tokenize all our tweets and take a look at the longest tokens in our data.

Spacy is an open-source NLP library that is much faster than the Natural Language Toolkit, although it does not have as many tasks implemented. You can find more information in the Spacy documentation.

# create a Spacy document of our tweets
# load an English-language Spacy model
nlp = spacy.load("en")

# apply the english language model to our tweets
doc = nlp(' '.join(tweetsData['Tweet']))

Now let’s look at the longest tokens in our Twitter data.

sorted(doc, key=len, reverse=True)[0:5]
[a7e78d48888a6811d84e0759e9387647447d1e74d8c7c4f1bec00d318e4e5030f08eb35668a97873820ca1d9dc61ffb620f8992296f3b029a60f153beac8018f5fb77d000000,
 e44337d70d7a7fec79a8b6bd8aa573367224023e4272f22af6d0844d9682d5b48062e331b33ab3b92dac2c262ed4f154ba679ad07b30d2cf1c15851cdac901315b4e72000000,
 3064d36c909f9d437f7a3f405aa550f65529566547ae2308d6c4f2585250106d33b924ae9c8dcc08856e41f611d9bd15409a79f7ba21d318ab484f0cae10017201590a000000,
 69bdf5177f1ae8ed61ed71c477f7dc415b97a2b2d7e57be079feb1a2c52600a996fd0891e130c1ce13c94e4406f83ba59e5edb5a7e0fb45e5251a17bb29601081f3de0000000,
 lt;3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3]

The five longest tokens are entire tweets, four produced by an art bot that tweets hashes of Unix timestamps and one that’s just the HTML version of “<3” tweeted a bunch of times. In other words: normal Twitter weirdness. This is actual noise in the data and can be safely discarded without hurting downstream tasks, like sentiment analysis or topic modeling.

sorted(doc, key=len, reverse=True)[6:10]
[卒業したった(*^^*)\n彼女にクラスで一緒にいるやつに\nたった一人の同中の拓夢とも写真撮れたし満足や!(^。^)時間ギリギリまでテニスやってたからテニス部面と写真撮ってねーわ‼︎まぁこいつらわこれからも付き合いあるだろうからいいか!,
 眼鏡は近視用で黒のセルフレームかアンダーリムでお願いします。オフの日は赤いセルフレームです。形状はサークルでお願いします。30代前半です。髪型ボブカットもしくはティモシェンコ元ウクライナ首相みたいなので。色は黒目でとりあえずお願いします,
 普段は写真撮られるの苦手なので、\n\n顔も出さずw\n\n登場回数少ないですが、\n\n元気にampで働いておりますw\n\n一応こんな人が更新してますのでw\n\n#takahiromiyashitathesolois,
 love#instagood#me#cute#tbt#photooftheday#instamood#tweegram#iphonesia#picoftheday#igers#summer#girl#insta]

The next five longest tokens are also whole tweets which have been identified as single tokens. In this case, though, they were produced by humans!

The tokenizer (which assumes it will be given mainly English data) fails to correct tokenize these tweets because it’s looking for spaces. These tweets are in Japanese, though, and like many Asian languages (including all varieties of Chinese, Korean and Thai) they don’t actually use spaces between words.

In case you’re curious, “、” and “。” are single characters and don’t contain spaces! They are, respectively, the ideographic comma and ideographic full stop, and are part of a very long list of line breaking characters associated with specific orthographic systems.

In order to correctly tokenize Japanese, you’ll need to use a language-specific tokenizer.

The takeaway: if you ignore multiple languages, you’ll end up violating the assumptions behind major out-of-the-box NLP tools


Option 2: Only look at the parts of the data that are in English

So we know that just applying NLP tools designed for English willy-nilly won’t work on multiple languages. So what if we only grabbed the English-language data and then worked with that?

There are two big issues here:

  • Correctly identifying which tweets are in English
  • Throwing away data

Correctly identifying which tweets are in English

Probably the least time-intensive way to do this is by attempting to automatically identify the language that each Tweet is written in. A BIG grain of salt here: automatic language identifiers are very error prone, especially on very short texts. Let’s check out two of them.

  • LangID: Lui, Marco and Timothy Baldwin (2011) Cross-domain Feature Selection for Language Identification, In Proceedings of the Fifth International Joint Conference on Natural Language Processing (IJCNLP 2011), Chiang Mai, Thailand, pp. 553—561. Available from http://www.aclweb.org/anthology/I11-1062
  • TextCat: Cavnar, W. B. and J. M. Trenkle, “N-Gram-Based Text Categorization” In Proceedings of Third Annual Symposium on Document Analysis and Information Retrieval, Las Vegas, NV, UNLV Publications/Reprographics, pp. 161-175, 11-13 April 1994.

First off, here are the languages the first five tweets are actually written in, hand tagged by a linguist (i.e. me):

  1. Turkish
  2. Turkish
  3. English
  4. English
  5. English

Now let’s see how well two popular language identifiers can detect this.

# summerize the labelled language
tweetsData['Tweet'][0:5].apply(langid.classify)
0     (az, -30.30187177658081)
1     (ms, -83.29260611534119)
2      (en, 9.061840057373047)
3    (en, -195.55468368530273)
4     (en, -98.53013229370117)
Name: Tweet, dtype: object

LangID does…alright, with three out of five tweets identified correctly. While it’s pretty good at identifying English, the first tweet was identified as Azerbaijani and the second tweet was labeled as Malay, which is very wrong (not even in the same language family as Turkish).

Let’s look at another algorithm, TextCat, which is based on character-level N-Grams.

# N-Gram-Based Text Categorization
tc = TextCat()

# try to identify the languages of the first five tweets again
tweetsData['Tweet'][0:5].apply(tc.guess_language)
0    tur
1    ind
2    bre
3    eng
4    eng
Name: Tweet, dtype: object

TextCat also only got three out of the five correct. Oddly, it identifier “bed” as Breton. To be fair, “bed” is the Breton word for “world”, but it’s still a bit odd.

The takeaway: Automatic language identification, especially on very short texts, is very error prone. (I’d recommend using multiple language identifiers & taking the majority vote.)

Throwing away data

Even if language identification were very accurate, how much data would be just be throwing away if we only looked at data we were fairly sure was English?

Note: I’m only going to LangID here for time reasons, but given the high error rate I’d recommend using multiple language identification algorithms.

# get the language id for each text
ids_langid = tweetsData['Tweet'].apply(langid.classify)

# get just the language label
langs = ids_langid.apply(lambda tuple: tuple[0])

# how many unique language labels were applied?
print("Number of tagged languages (estimated):")
print(len(langs.unique()))

# percent of the total dataset in English
print("Percent of data in English (estimated):")
print((sum(langs=="en")/len(langs))*100)
Number of tagged languages (estimated):
95
Percent of data in English (estimated):
40.963625976

Only 40% of our data has been tagged as English by LangId. If we throw the rest of it, we’re going to lose more than half of our dataset! Especially if this is data you spent a lot of time and money collecting, that seems downright wasteful. (Plus, it might skew our analysis.)

So if 40% of our data is in English, what is the other 60% made up of? Let’s check out the distribution data across languages in our dataset.

# convert our list of languages to a dataframe
langs_df = pd.DataFrame(langs)

# count the number of times we see each language
langs_count = langs_df.Tweet.value_counts()

# horrible-looking barplot (I would suggest using R for visualization)
langs_count.plot.bar(figsize=(20,10), fontsize=20)

There’s a really long tail on our dataset; most that were identified in our dataset were only identified a few times. This means that we can get a lot of mileage out of including just a few more popular languages in our analysis. How much will we gain, exactly?

print("Languages with more than 400 tweets in our dataset:")
print(langs_count[langs_count > 400])

print("")

print("Percent of our dataset in these languages:")
print((sum(langs_count[langs_count > 400])/len(langs)) * 100)
Languages with more than 400 tweets in our dataset:
en    4302
es    1020
pt     751
ja     436
tr     414
id     407
Name: Tweet, dtype: int64

Percent of our dataset in these languages:
69.7962292897

By including only five more languages in our analysis (Spanish, Portugese, Japanese, Turkish and Indonesian) we can increase our coverage of the data in our dataset by almost a third!

The takeaway: Just incorporating a couple more languages in your analysis can give you access to a lot more data!


Option 3: Break the data apart by language & use language-specific tools

Ok, so what exactly does this pipeline look like? Let’s look at just the second most popular language in our dataset: Spanish. What happens when we pull out just the Spanish tweets & tokenize them?

# get a list of tweets labelled "es" by langid
spanish_tweets = tweetsData['Tweet'][langs == "es"]

# load a Spanish-language Spacy model
from spacy.es import Spanish
nlp_es = Spanish(path=None)

# apply the Spanish language model to our tweets
doc_es = nlp_es(' '.join(spanish_tweets))

# print the longest tokens
sorted(doc_es, key=len, reverse=True)[0:5]
[ViernesSantoEnElColiseoRobertoClemente,
 MiFantasia1DEnWembleyConCocaColaFM,
 fortaleciéndonos','escenarios,
 DirectionersConCocaColaFM1D,
 http://t.co/ezZEsXN3MF\nvia]

This time, the longest tokens are Spanish-language hashtags. This is exactly the sort of thing we’d expect to see! From here, we can use this tokenized dataset to feed into other downstream like sentiment analysis.

Of course, it would be impractical to do this for every single language in our dataset, even if we could be sure that they were all identified correctly. You’re probably going to have to accept that you probably won’t be able to consider every language in your dataset unless you can commit a lot of time. But including any additional language will enrich your analysis!

The takeaway: It doesn’t have to be onerous to incorporate multiple languages in your analysis pipeline!


So let’s review our options for analyzing multilingual data:

Option 1: Ignore Multilingualism

As we saw, this option will result in violating a lot of the assumptions built into NLP tools (e.g. there are spaces between words). If you do this, you’ll end up with a lot of noise and headaches as you try to move through your analysis pipeline.

Option 2: Only look at English

In this dataset, only looking at English would have led to us throwing away over half of our data. Especailly as NLP tools are developed and made avaliable for more and more languages, there’s less reason to stick to English-only NLP.

Option 3: Seperate your data by language & analyze them independently

This does take a little more work than the other options… but not that much more, especially for languages that already have resources avalialbe for them.

Additional resources:

Language Identification:

Here are some pre-built language identifiers to use in addition to LandID and TextCat:

Dealing with texts which contain multiple languages (code switching):

It’s very common for a span of text to include multiple languages. This example contains English and Malay (“kain kain” is Malay for “unwrap”):

Roasted Chicken Rice with Egg. Kain kain! 🙂 [Image of a lunch wrapped in paper being unwrapped.]

How to automatically handle code switching is an active research question in NLP. Here are some resources to get you started learning more: