fastText是一个用于高效学习词表示和句子分类的库

# fastText [](https://circleci.com/gh/facebookresearch/fastText/tree/master) [fastText](https://fasttext.cc/) is a library for efficient learning of word representations and sentence classification. In this document we present how to use fastText in python. ## Table of contents * [Requirements](#requirements) * [Installation](#installation) * [Usage overview](#usage-overview) * [Word representation model](#word-representation-model) * [Text classification model](#text-classification-model) * [IMPORTANT: Preprocessing data / encoding conventions](#important-preprocessing-data-encoding-conventions) * [More examples](#more-examples) * [API](#api) * [`train_unsupervised` parameters](#train_unsupervised-parameters) * [`train_supervised` parameters](#train_supervised-parameters) * [`model` object](#model-object) # Requirements [fastText](https://fasttext.cc/) builds on modern Mac OS and Linux distributions. Since it uses C\++11 features, it requires a compiler with good C++11 support. You will need [Python](https://www.python.org/) (version 2.7 or ≥ 3.4), [NumPy](http://www.numpy.org/) & [SciPy](https://www.scipy.org/) and [pybind11](https://github.com/pybind/pybind11). # Installation To install the latest release, you can do : ```bash $ pip install fasttext ``` or, to get the latest development version of fasttext, you can install from our github repository : ```bash $ git clone https://github.com/facebookresearch/fastText.git $ cd fastText $ sudo pip install . $ # or : $ sudo python setup.py install ``` # Usage overview ## Word representation model In order to learn word vectors, as [described here](https://fasttext.cc/docs/en/references.html#enriching-word-vectors-with-subword-information), we can use `fasttext.train_unsupervised` function like this: ```py import fasttext # Skipgram model : model = fasttext.train_unsupervised('data.txt', model='skipgram') # or, cbow model : model = fasttext.train_unsupervised('data.txt', model='cbow') ``` where `data.txt` is a training file containing utf-8 encoded text. The returned `model` object represents your learned model, and you can use it to retrieve information. ```py print(model.words) # list of words in dictionary print(model['king']) # get the vector of the word 'king' ``` ### Saving and loading a model object You can save your trained model object by calling the function `save_model`. ```py model.save_model("model_filename.bin") ``` and retrieve it later thanks to the function `load_model` : ```py model = fasttext.load_model("model_filename.bin") ``` For more information about word representation usage of fasttext, you can refer to our [word representations tutorial](https://fasttext.cc/docs/en/unsupervised-tutorial.html). ## Text classification model In order to train a text classifier using the method [described here](https://fasttext.cc/docs/en/references.html#bag-of-tricks-for-efficient-text-classification), we can use `fasttext.train_supervised` function like this: ```py import fasttext model = fasttext.train_supervised('data.train.txt') ``` where `data.train.txt` is a text file containing a training sentence per line along with the labels. By default, we assume that labels are words that are prefixed by the string `__label__` Once the model is trained, we can retrieve the list of words and labels: ```py print(model.words) print(model.labels) ``` To evaluate our model by computing the precision at 1 (P@1) and the recall on a test set, we use the `test` function: ```py def print_results(N, p, r): print("N\t" + str(N)) print("P@{}\t{:.3f}".format(1, p)) print("R@{}\t{:.3f}".format(1, r)) print_results(*model.test('test.txt')) ``` We can also predict labels for a specific text : ```py model.predict("Which baking dish is best to bake a banana bread ?") ``` By default, `predict` returns only one label : the one with the highest probability. You can also predict more than one label by specifying the parameter `k`: ```py model.predict("Which baking dish is best to bake a banana bread ?", k=3) ``` If you want to predict more than one sentence you can pass an array of strings : ```py model.predict(["Which baking dish is best to bake a banana bread ?", "Why not put knives in the dishwasher?"], k=3) ``` Of course, you can also save and load a model to/from a file as [in the word representation usage](#saving-and-loading-a-model-object). For more information about text classification usage of fasttext, you can refer to our [text classification tutorial](https://fasttext.cc/docs/en/supervised-tutorial.html). ### Compress model files with quantization When you want to save a supervised model file, fastText can compress it in order to have a much smaller model file by sacrificing only a little bit performance. ```py # with the previously trained `model` object, call : model.quantize(input='data.train.txt', retrain=True) # then display results and save the new model : print_results(*model.test(valid_data)) model.save_model("model_filename.ftz") ``` `model_filename.ftz` will have a much smaller size than `model_filename.bin`. For further reading on quantization, you can refer to [this paragraph from our blog post](https://fasttext.cc/blog/2017/10/02/blog-post.html#model-compression). ## IMPORTANT: Preprocessing data / encoding conventions In general it is important to properly preprocess your data. In particular our example scripts in the [root folder](https://github.com/facebookresearch/fastText) do this. fastText assumes UTF-8 encoded text. All text must be [unicode for Python2](https://docs.python.org/2/library/functions.html#unicode) and [str for Python3](https://docs.python.org/3.5/library/stdtypes.html#textseq). The passed text will be [encoded as UTF-8 by pybind11](https://pybind11.readthedocs.io/en/master/advanced/cast/strings.html?highlight=utf-8#strings-bytes-and-unicode-conversions) before passed to the fastText C++ library. This means it is important to use UTF-8 encoded text when building a model. On Unix-like systems you can convert text using [iconv](https://en.wikipedia.org/wiki/Iconv). fastText will tokenize (split text into pieces) based on the following ASCII characters (bytes). In particular, it is not aware of UTF-8 whitespace. We advice the user to convert UTF-8 whitespace / word boundaries into one of the following symbols as appropiate. * space * tab * vertical tab * carriage return * formfeed * the null character The newline character is used to delimit lines of text. In particular, the EOS token is appended to a line of text if a newline character is encountered. The only exception is if the number of tokens exceeds the MAX\_LINE\_SIZE constant as defined in the [Dictionary header](https://github.com/facebookresearch/fastText/blob/master/src/dictionary.h). This means if you have text that is not separate by newlines, such as the [fil9 dataset](http://mattmahoney.net/dc/textdata), it will be broken into chunks with MAX\_LINE\_SIZE of tokens and the EOS token is not appended. The length of a token is the number of UTF-8 characters by considering the [leading two bits of a byte](https://en.wikipedia.org/wiki/UTF-8#Description) to identify [subsequent bytes of a multi-byte sequence](https://github.com/facebookresearch/fastText/blob/master/src/dictionary.cc). Knowing this is especially important when choosing the minimum and maximum length of subwords. Further, the EOS token (as specified in the [Dictionary header](https://github.com/facebookresearch/fastText/blob/master/src/dictionary.h)) is considered a character and will not be broken into subwords. ## More examples In order to have a better knowledge of fastText models, please consider the main [README](https://github.com/facebookresearch/fastText/blob/master/README.md) and in particular [the tutorials on our website](https://fasttext.cc/docs/en/supervi