Find the most frequent item of an array (not just strings)

Question

Can someone walk me through this exercise? Write a JavaScript program to find the most frequent item of an array.

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Answer 1

This is an answer to point (3) using underscore:

function length(a) { return a.length; }

_.max(_.groupBy(arr1), length)[0]

How this works:

> arr1 = [3, 'a', 'a', 'a', 2, 3, 'a', 3, 'a', 2, 4, 9, 3];

> groups = _.groupBy(arr1)
< { 2: [2,2], 3: [3,3,3,3], 4: [4], 9: [9], a: ['a', 'a', ...] }

> max_group = _.max(groups, length)
< ['a', 'a', ...]

> max_group [0]
< 'a'