Custom Python Evaluation Metric | Dataford Interview Questions

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Problem

NTT DATA evaluates binary classification outputs from AI solutions. Implement a custom F1-score metric from scratch using only basic Python arrays and arithmetic, without importing machine learning libraries.

Given two arrays, y_true and y_pred, containing binary labels, calculate the F1-score:

F1 = 2 * TP / (2 * TP + FP + FN)

Count true positives, false positives, and false negatives during one pass through the arrays. True negatives do not affect the F1-score. If the denominator is zero, return 0.0.

Formal Specification

Input: Two arrays of integers, y_true and y_pred, with equal length. Each value is either 0 or 1.
Output: A floating-point F1-score between 0.0 and 1.0.
Do not round the result inside the function.

Constraints

1 <= len(y_true) <= 10^6
len(y_true) == len(y_pred)
Each value in both arrays is either 0 or 1
Return 0.0 when TP + FP + FN is zero

Function Signature

def binary_f1_score(y_true, y_pred):