Licensed under the MIT License.

Interpreting Classical Text Classification models

This notebook showcases how to use the interpret-text repo to implement an interpretable module using feature importances and bag of words representation.

Contents

  1. Introduction
  2. Setup
  3. Training
  4. Results
In [ ]:
import sys
sys.path.append("../..")
import os

# sklearn
from sklearn.metrics import precision_recall_fscore_support
from sklearn.model_selection import train_test_split
from sklearn.preprocessing import LabelEncoder

from interpret_text.experimental.classical import ClassicalTextExplainer

from notebooks.test_utils.utils_mnli import load_mnli_pandas_df

# for testing
from scrapbook.api import glue

working_dir = os.getcwd()

1. Introduction

This notebook illustrates how to locally use interpret-text to help interpret text classification using a logisitic regression baseline and bag of words encoding. It demonstrates the API calls needed to obtain the feature importances along with a visualization dashbard.

Note:
  • Although we use logistic regression, any model that follows sklearn's classifier API should be supported natively or with minimal tweaking.
  • The interpreter supports interpretations using either coefficients associated with linear models or feature importances associated with ensemble models.
  • The classifier relies on scipy's sparse representations to keep the dataset in memory.

2. Setup

The notebook is built on features made available by scikit-learn and spacy for easier compatibiltiy with popular tookits.

Configuration parameters

In [ ]:
DATA_FOLDER = './temp'
TRAIN_SIZE = 0.7
TEST_SIZE = 0.3

Data loading

In [ ]:
df = load_mnli_pandas_df(DATA_FOLDER, "train")
df = df[df["gold_label"] == "neutral"]  # get unique sentences

# fetch documents and labels from data frame
X_str = df['sentence1']  # the document we want to analyze
ylabels = df['genre'] # the labels, or answers, we want to test against

Create explainer

In [ ]:
# Create explainer object that contains default glassbox classifier and explanation methods
explainer = ClassicalTextExplainer()
label_encoder = LabelEncoder()

Training

Note: Vocabulary
  • The vocabulary is compiled from the training set. Any word that does not appear in the training data split, will not appear in the vocabulary.
  • The word must appear one or more times to be considered part of the vocabulary.
  • However, the sklearn countvectorizer allows the addition of a custom vocabulary as an input parameter.

Configure training setup

This step will cast the training data and labels into the correct format

  1. Split data into train and test using a random shuffle
  2. Load desired classifier. In this case, Logistic Regression is set as default.
  3. Setup grid search for hyperparameter optimization and train model. Edit the hyper parameter range to search over as per your model.
  4. Fit models to train set
In [ ]:
X_train, X_test, y_train, y_test = train_test_split(X_str, ylabels, train_size=0.8, test_size=0.2)
y_train = label_encoder.fit_transform(y_train)
y_test = label_encoder.transform(y_test)
In [ ]:
print("X_train shape =" + str(X_train.shape))
print("y_train shape =" + str(y_train.shape))
print("X_train data structure = " + str(type(X_train)))

Model Overview

The 1-gram Bag of Words allows a 1:1 mapping from individual words to their respective frequencies in the document-term matrix.

In [ ]:
classifier, best_params = explainer.fit(X_train, y_train)

Results

Notes for default Logistic Regression classifier:
  • The parameters are set using cross-validation
  • Below listed hyperparamters are selected by searching over a larger space.
  • These apply specifically to this instance of the logistic regression model and mnli dataset.
  • 'Multinomial' setup was found to be better than 'one-vs-all' across the board
  • Default 'liblinear' solver is not supported for 'multinomial' model setup
  • For a different model or dataset, set the range as appropriate using the hyperparam_range argument in the train method
In [ ]:
# obtain best classifier and hyper params
print("best classifier: " + str(best_params))

Performance Metrics

In [ ]:
mean_accuracy = classifier.score(X_test, y_test, sample_weight=None)
print("accuracy = " + str(mean_accuracy * 100) + "%")
y_pred = classifier.predict(X_test)
[precision, recall, fscore, support] = precision_recall_fscore_support(y_test, y_pred,average='macro')

Capture metrics for integration testing

In [ ]:
glue("accuracy", mean_accuracy)
glue("precision", precision)
glue("recall", recall)
glue("f1", fscore)
print("[precision, recall, fscore, support] = " + str([precision, recall, fscore, support]))

Local Importances

Local importances are the most and least important words for a single document.

In [ ]:
# Enter any document or a document and label pair that needs to be interpreted
document = "I travelled to the beach. I took the train. I saw fairies, dragons and elves"
document1 = "The term construction means fabrication, erection, or installation of an affected unit."
document2 = "Demonstrating Product Reliability Indicates the Product Is Ready for Production"
document3 = "and see there\'s no secrecy to that because the bill always comes in and we know how much they pay for it"
document4 = "Had that piquant gipsy face been at the bottom of the crime, or was it 73 the baser mainspring of money?"
document5 = "No, the boy trusted me, and I shan\'t let him down."
In [ ]:
# Obtain the top feature ids for the selected class label
explainer.preprocessor.labelEncoder = label_encoder
In [ ]:
local_explanation = explainer.explain_local(document)

Alternatively, you can pass the predicted label with the document

In [ ]:
y = classifier.predict(document1)
predicted_label = label_encoder.inverse_transform(y)
local_explanation = explainer.explain_local(document1, predicted_label)
In [ ]:
from interpret_text.experimental.widget import ExplanationDashboard
In [ ]:
ExplanationDashboard(local_explanation)