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x/ramda/countBy.js

:ram: Practical functional Javascript
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import reduceBy from './reduceBy';

/** * 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. * * @func * @memberOf R * @since v0.1.0 * @category Relation * @sig (a -> String) -> [a] -> {*} * @param {Function} fn The function used to map values to keys. * @param {Array} list The list to count elements from. * @return {Object} An object mapping keys to number of occurrences in the list. * @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} */var countBy = reduceBy(function(acc, elem) { return acc + 1; }, 0);export default countBy;