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var createAggregator = require('../internal/createAggregator');
/** Used for native method references. */
var objectProto = Object.prototype;
/** Used to check objects for own properties. */
var hasOwnProperty = objectProto.hasOwnProperty;
/**
* Creates an object composed of keys generated from the results of running
* each element of `collection` through `iteratee`. The corresponding value
* of each key is the number of times the key was returned by `iteratee`.
* The `iteratee` is bound to `thisArg` and invoked with three arguments:
* (value, index|key, collection).
*
* If a property name is provided for `iteratee` the created `_.property`
* style callback returns the property value of the given element.
*
* If a value is also provided for `thisArg` the created `_.matchesProperty`
* style callback returns `true` for elements that have a matching property
* value, else `false`.
*
* If an object is provided for `iteratee` the created `_.matches` style
* callback returns `true` for elements that have the properties of the given
* object, else `false`.
*
* @static
* @memberOf _
* @category Collection
* @param {Array|Object|string} collection The collection to iterate over.
* @param {Function|Object|string} [iteratee=_.identity] The function invoked
* per iteration.
* @param {*} [thisArg] The `this` binding of `iteratee`.
* @returns {Object} Returns the composed aggregate object.
* @example
*
* _.countBy([4.3, 6.1, 6.4], function(n) {
* return Math.floor(n);
* });
* // => { '4': 1, '6': 2 }
*
* _.countBy([4.3, 6.1, 6.4], function(n) {
* return this.floor(n);
* }, Math);
* // => { '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);
});
module.exports = countBy;
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