lodash/lodash.countby/index.js

/**
 * lodash 4.3.0 (Custom Build) <https://lodash.com/>
 * Build: `lodash modularize exports="npm" -o ./`
 * Copyright jQuery Foundation and other contributors <https://jquery.org/>
 * Released under MIT license <https://lodash.com/license>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 */
var baseEach = require('lodash._baseeach'),
    baseIteratee = require('lodash._baseiteratee');

/**
 * A specialized version of `baseAggregator` for arrays.
 *
 * @private
 * @param {Array} array The array to iterate over.
 * @param {Function} setter The function to set `accumulator` values.
 * @param {Function} iteratee The iteratee to transform keys.
 * @param {Object} accumulator The initial aggregated object.
 * @returns {Function} Returns `accumulator`.
 */
function arrayAggregator(array, setter, iteratee, accumulator) {
  var index = -1,
      length = array.length;

  while (++index < length) {
    var value = array[index];
    setter(accumulator, value, iteratee(value), array);
  }
  return accumulator;
}

/** Used for built-in method references. */
var objectProto = Object.prototype;

/** Used to check objects for own properties. */
var hasOwnProperty = objectProto.hasOwnProperty;

/**
 * Aggregates elements of `collection` on `accumulator` with keys transformed
 * by `iteratee` and values set by `setter`.
 *
 * @private
 * @param {Array|Object} collection The collection to iterate over.
 * @param {Function} setter The function to set `accumulator` values.
 * @param {Function} iteratee The iteratee to transform keys.
 * @param {Object} accumulator The initial aggregated object.
 * @returns {Function} Returns `accumulator`.
 */
function baseAggregator(collection, setter, iteratee, accumulator) {
  baseEach(collection, function(value, key, collection) {
    setter(accumulator, value, iteratee(value), collection);
  });
  return accumulator;
}

/**
 * Creates a function like `_.groupBy`.
 *
 * @private
 * @param {Function} setter The function to set accumulator values.
 * @param {Function} [initializer] The accumulator object initializer.
 * @returns {Function} Returns the new aggregator function.
 */
function createAggregator(setter, initializer) {
  return function(collection, iteratee) {
    var func = isArray(collection) ? arrayAggregator : baseAggregator,
        accumulator = initializer ? initializer() : {};

    return func(collection, setter, baseIteratee(iteratee), accumulator);
  };
}

/**
 * Creates an object composed of keys generated from the results of running
 * each element of `collection` thru `iteratee`. The corresponding value of
 * each key is the number of times the key was returned by `iteratee`. The
 * iteratee is invoked with one argument: (value).
 *
 * @static
 * @memberOf _
 * @since 0.5.0
 * @category Collection
 * @param {Array|Object} collection The collection to iterate over.
 * @param {Array|Function|Object|string} [iteratee=_.identity]
 *  The iteratee to transform keys.
 * @returns {Object} Returns the composed aggregate object.
 * @example
 *
 * _.countBy([6.1, 4.2, 6.3], Math.floor);
 * // => { '4': 1, '6': 2 }
 *
 * _.countBy(['one', 'two', 'three'], 'length');
 * // => { '3': 2, '5': 1 }
 */
var countBy = createAggregator(function(result, value, key) {
  hasOwnProperty.call(result, key) ? ++result[key] : (result[key] = 1);
});

/**
 * Checks if `value` is classified as an `Array` object.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @type {Function}
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is correctly classified,
 *  else `false`.
 * @example
 *
 * _.isArray([1, 2, 3]);
 * // => true
 *
 * _.isArray(document.body.children);
 * // => false
 *
 * _.isArray('abc');
 * // => false
 *
 * _.isArray(_.noop);
 * // => false
 */
var isArray = Array.isArray;

module.exports = countBy;