ndg-tools

I developed the tools in this package for my own use on data science projects. They are in an early stage of development and not intended for public use. Nevertheless, you are free to install them.

pip install git+https://github.com/ndgigliotti/ndg-tools.git@main

Important Modules

language

One of the most extensive modules in the package is ndg_tools.language, which contains string processing functions, token processing functions, n-gram search functions, and other utilities.

language.processors

A number of text (str) and token (list of str) processing functions can be found in ndg_tools.language.processors. For example, strip_html_tags thoroughly removes HTML tags from strings. All of the text processing functions are polymorphic, meaning that they behave differently according to the type of object passed to them. They work on singular strings as well as string-containers such as lists, sets, ndarrays, Series, or DataFrames.

All of the text and token processors feature optional parallel processing, implemented with joblib. Parallel processing can be activated using the n_jobs keyword argument. For example, passing n_jobs=-1 sets the number of jobs to the number of available cores. In a future update, the batch size will also be adjustable in every function.

All of the text and token processors have a built-in tqdm progress bar which will appear in Jupyter Notebooks. The progress bar only appears when the function is used on a string container object.

Several functions can be chained together in a pipeline using the make_preprocessor function. The function chain will be applied to each string independently, no matter what object type is passed.

language.ngrams

Inside ndg_tools.language.ngrams are functional wrappers of the nltk collocation search tools. There is also a stratified_ngrams function, which allows for collocation-searching relative to a categorical variable. In other words, the documents are grouped by a categorical variable and each group is scanned independently for collocations.

sklearn

The ndg_tools.sklearn module contains tools related to Scikit-Learn and the Scikit-Learn API. Currently it contains a universal hyperparameter optimization function called sweep, and some custom text vectorizers such as VaderVectorizer and FreqVectorizer.

sklearn.selection.sweep

The purpose of the sweep function is to provide a flexible interface to all of Scikit-Learn's hyperparameter optimization objects. The function itself has many parameters, which some may see as excessively complex. However, there are a number of benefits:

• Easily switch between different search types by setting kind to 'grid', 'rand', 'hgrid', or 'hrand'.
• Immediately pickle the search estimator or CV results when the search is finished.
• Add a prefix such as 'col__vec__' to the entire hyperparameter space specification.
• Specify the hyperparameter space with Series objects in addition to lists and dicts.
• Hold some parameters in place for repeat use with functools.partial.

sklearn.vectorizers.VaderVectorizer

VADER (Valence Aware Dictionary and sEntiment Reasoner) is a rule-based sentiment analysis tool which assigns polarity scores to a short piece of text. While NLTK provides a nice implementation of VADER, I like to integrate my feature extraction/engineering with the Scikit-Learn API so it can be tuned and tested alongside the model. VaderVectorizer is simply a text vectorizer which extracts the four VADER polarity scores: negative, neutral, positive, and compound. It is intended to be used in a FeatureUnion with another vectorizer.

sklearn.vectorizers.FreqVectorizer

Because Scikit-Learn's CountVectorizer and TfidfVectorizer offer only a few preprocessing options, I extended them with many more. Sometimes preprocessing steps must be taken to avoid overfitting, but sometimes they are open to optimization. The new preprocessing options utilize functions in the ndg_tools.language module.

One new preprocessing step which is enabled by default is decoding HTML entities like & or —. These codes for punctuation symbols appear frequently in text, and are liable to become noise if not decoded.

Another preprocessing option for use in sentiment analysis is negation-marking. Setting mark_negation=True, tells the vectorizer to mark terms '_NEG' which appear between a negation term and sentential punctuation.

Note that while FreqVectorizer is a subclass of TfidfVectorizer, it is set to act as a CountVectorizer by default. IDF weighting, binarization, normalization, and other options can be easily activated.

outliers

The ndg_tools.outliers module provides a number of tools for dealing with outliers. The three basic approaches to outlier detection in that module are the IQR proximity rule, the Z-score method (i.e. standard score), and simple quantile-based detection.

The detection methods are combined with ways of dealing with outliers once detected. There are two different options: trimming or Winsorization. Trimming is the traditional approach of dropping outliers from the dataset. Winsorization, on the other hand, means resetting each outlying value to the value of the nearest inlier. Winsorization reduces the influence of outliers without throwing away entire observations (i.e. rows of the table).

To Do

• Write more tests to attain complete test coverage of the package.
• Clean up and standardize ndg_tools.plotting.
• Develop a subset of the tools into a specialized package for public use.