MediumNLPnlp-026

Perplexity from Probabilities

Problem

Return the perplexity of a sequence of probabilities: exp of the negative mean log probability, that is exp(-(sum(log(p)) / N)).

Return 1.0 for an empty list.

Hint

Average the log probabilities first, then undo the mean with exp.

case 1

in: [[0.5,0.5]]

expected: 2

case 2

in: [[0.25,0.25,0.25,0.25]]

expected: 4

case 3

in: [[1,1]]

expected: 1

case 4

in: [[0.5,0.25]]

expected: 2.82842712474619

case 5

in: [[]]

expected: 1

Starter codePython

import math
def perplexity(probs):
    # Your code here
    pass

5 test cases · run your code against them in the editor