shopping.py

import csv
import pandas
import sys

from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier
from sklearn.metrics import confusion_matrix

TEST_SIZE = 0.4


def main():

    # Check command-line arguments
    if len(sys.argv) != 2:
        sys.exit("Usage: python shopping.py data")

    # Load data from spreadsheet and split into train and test sets
    evidence, labels = load_data(sys.argv[1])
    X_train, X_test, y_train, y_test = train_test_split(
        evidence, labels, test_size=TEST_SIZE
    )

    # Train model and make predictions
    model = train_model(X_train, y_train)
    predictions = model.predict(X_test)
    sensitivity, specificity = evaluate(y_test, predictions)

    # Print results
    print(f"Correct: {(y_test == predictions).sum()}")
    print(f"Incorrect: {(y_test != predictions).sum()}")
    print(f"True Positive Rate: {100 * sensitivity:.2f}%")
    print(f"True Negative Rate: {100 * specificity:.2f}%")


def load_data(filename):
    """
    Load shopping data from a CSV file `filename` and convert into a list of
    evidence lists and a list of labels. Return a tuple (evidence, labels).

    evidence should be a list of lists, where each list contains the
    following values, in order:
        - Administrative, an integer
        - Administrative_Duration, a floating point number
        - Informational, an integer
        - Informational_Duration, a floating point number
        - ProductRelated, an integer
        - ProductRelated_Duration, a floating point number
        - BounceRates, a floating point number
        - ExitRates, a floating point number
        - PageValues, a floating point number
        - SpecialDay, a floating point number
        - Month, an index from 0 (January) to 11 (December)
        - OperatingSystems, an integer
        - Browser, an integer
        - Region, an integer
        - TrafficType, an integer
        - VisitorType, an integer 0 (not returning) or 1 (returning)
        - Weekend, an integer 0 (if false) or 1 (if true)

    labels should be the corresponding list of labels, where each label
    is 1 if Revenue is true, and 0 otherwise.
    """

    evidence = []
    labels = []

    months = {'Jan': 0,
              'Feb': 1,
              'Mar': 2,
              'Apr': 3,
              'May': 4,
              'June': 5,
              'Jul': 6,
              'Aug': 7,
              'Sep': 8,
              'Oct': 9,
              'Nov': 10,
              'Dec': 11}

    # read csv file
    csv_file = pandas.read_csv(filename)

    # prepare labels dataframe
    labels_df = csv_file['Revenue']

    # prepare evidence dataframe
    evidence_df = csv_file.drop(columns=['Revenue'])

    # replace month names with numerical values
    evidence_df = evidence_df.replace(months)

    # replace boolean with 0/1 values
    evidence_df['VisitorType'] = evidence_df['VisitorType'].apply(lambda x: 1 if x == 'Returning_Visitor' else 0)
    evidence_df['Weekend'] = evidence_df['Weekend'].apply(lambda x: 1 if x == 'True' else 0)
    labels_df = labels_df.apply(lambda x: 1 if x is True else 0)

    # convert dataframes to lists
    evidence_list = evidence_df.values.tolist()
    labels_list = labels_df.values.tolist()

    return evidence_list, labels_list


def train_model(evidence, labels):
    """
    Given a list of evidence lists and a list of labels, return a
    fitted k-nearest neighbor model (k=1) trained on the data.
    """

    neigh = KNeighborsClassifier(n_neighbors=1)
    neigh.fit(evidence, labels)
    return neigh


def evaluate(labels, predictions):
    """
    Given a list of actual labels and a list of predicted labels,
    return a tuple (sensitivity, specificty).

    Assume each label is either a 1 (positive) or 0 (negative).

    `sensitivity` should be a floating-point value from 0 to 1
    representing the "true positive rate": the proportion of
    actual positive labels that were accurately identified.

    `specificity` should be a floating-point value from 0 to 1
    representing the "true negative rate": the proportion of
    actual negative labels that were accurately identified.
    """
    tn, fp, fn, tp = confusion_matrix(labels, predictions).ravel()
    sensitivity = tp / (tp + fn)
    specificity = tn / (tn + fp)

    return sensitivity, specificity


if __name__ == "__main__":
    main()