count-by

v0.9.6

STATUS

Passing

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VISIBILITY

Public

PUBLISHED

5 years ago

SIZE

2 KB

Counts the elements of a list according to how many match each value of a key generated by the supplied function.

Counter

List

Utils

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countBy (

fn:Function,

list:Array

) : Object

Counts the elements of a list according to how many match each value of a key generated by the supplied function. Returns an object mapping the keys produced by fn to the number of occurrences in the list. Note that all keys are coerced to strings because of how JavaScript objects work.

Acts as a transducer if a transformer is given in list position.

Example

const numbers = [1.0, 1.1, 1.2, 2.0, 3.0, 2.2];
     R.countBy(Math.floor)(numbers);    //=> {'1': 3, '2': 2, '3': 1}

     const letters = ['a', 'b', 'A', 'a', 'B', 'c'];
     R.countBy(R.toLower)(letters);   //=> {'a': 3, 'b': 2, 'c': 1}

Arguments

fn: Function

The function used to map values to keys.

list: Array

The list to count elements from.

Returns

Object

An object mapping keys to number of occurrences in the list.