I wrote this blog post with the intention to review and compare some evaluation metrics typically used for classification tasks, and how they should be used depending on the dataset. I also show how one can tune the probability thresholds for particular metrics.

When you train a NER system the most typical evaluation method is to measure precision, recall and f1-score at a token level. These metrics are indeed useful to tune a NER system. But when using the predicted named-entities for downstream tasks, it is more useful to evaluate with metrics at a full named-entity level. In this post I will go through some metrics that go beyond simple token-level performance.

Convolutional Neural Networks (ConvNets) have in the past years shown break-through results in some NLP tasks, one particular task is sentence classification, i.e., classifying short phrases (i.e., around 20~50 tokens), into a set of pre-defined categories. In this post I will explain how ConvNets can be applied to classifying short-sentences and how to easily implemented them in Keras.

Sometimes your tokenization process is so complex that cannot be captured by a simple regular expression that you can pass to the scikit-learn TfidfVectorizer. Instead you just want to pass a list of tokens, resulting of a tokenization process, to initialize a TfidfVectorizer object.

I found myself, from time to time, always bumping into a piece of code (written by someone else) to perform grid search across different models in scikit-learn and always adapting it to suit my needs, and fixing it, since it contained some already deprecated calls. I finally decided to post it here in my blog, so I can quickly find it and also to share it with whoever needs it.

Stanford NER is a named-entity recognizer based on linear chain Conditional Random Field (CRF) sequence models. This post details some of the experiments I’ve done with it, using a corpus to train a Named-Entity Recognizer: the features I’ve explored (some undocumented), how to setup a web service exposing the trained model and how to call it from a python script.

This is the third and (maybe) the last part of a series of posts about sequential supervised learning applied to NLP. In this post I will talk about Conditional Random Fields (CRF), explain what was the main motivation behind the proposal of this model, and make a final comparison between Hidden Markov Models (HMM), Maximum Entropy Markov Models (MEMM) and CRF for sequence prediction.