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41 lines
1.2 KiB
JavaScript
41 lines
1.2 KiB
JavaScript
6 years ago
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var baseAssignValue = require('./_baseAssignValue'),
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createAggregator = require('./_createAggregator');
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/** Used for built-in method references. */
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var objectProto = Object.prototype;
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/** Used to check objects for own properties. */
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var hasOwnProperty = objectProto.hasOwnProperty;
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/**
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* Creates an object composed of keys generated from the results of running
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* each element of `collection` thru `iteratee`. The corresponding value of
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* each key is the number of times the key was returned by `iteratee`. The
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* iteratee is invoked with one argument: (value).
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*
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* @static
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* @memberOf _
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* @since 0.5.0
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* @category Collection
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* @param {Array|Object} collection The collection to iterate over.
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* @param {Function} [iteratee=_.identity] The iteratee to transform keys.
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* @returns {Object} Returns the composed aggregate object.
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* @example
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*
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* _.countBy([6.1, 4.2, 6.3], Math.floor);
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* // => { '4': 1, '6': 2 }
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*
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* // The `_.property` iteratee shorthand.
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* _.countBy(['one', 'two', 'three'], 'length');
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* // => { '3': 2, '5': 1 }
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*/
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var countBy = createAggregator(function(result, value, key) {
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if (hasOwnProperty.call(result, key)) {
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++result[key];
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} else {
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baseAssignValue(result, key, 1);
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}
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});
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module.exports = countBy;
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