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transform.js
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define(['../internal/arrayEach', '../internal/baseCallback', '../internal/baseCreate', '../internal/baseForOwn', '../lang/isArray', '../lang/isObject', '../lang/isTypedArray'], function(arrayEach, baseCallback, baseCreate, baseForOwn, isArray, isObject, isTypedArray) {
/**
* An alternative to `_.reduce`; this method transforms `object` to a new
* `accumulator` object which is the result of running each of its own enumerable
* properties through `iteratee`, with each invocation potentially mutating
* the `accumulator` object. The `iteratee` is bound to `thisArg` and invoked
* with four arguments; (accumulator, value, key, object). Iterator functions
* may exit iteration early by explicitly returning `false`.
*
* @static
* @memberOf _
* @category Object
* @param {Array|Object} object The object to iterate over.
* @param {Function} [iteratee=_.identity] The function invoked per iteration.
* @param {*} [accumulator] The custom accumulator value.
* @param {*} [thisArg] The `this` binding of `iteratee`.
* @returns {*} Returns the accumulated value.
* @example
*
* var squares = _.transform([1, 2, 3, 4, 5, 6], function(result, n) {
* n *= n;
* if (n % 2) {
* return result.push(n) < 3;
* }
* });
* // => [1, 9, 25]
*
* var mapped = _.transform({ 'a': 1, 'b': 2, 'c': 3 }, function(result, n, key) {
* result[key] = n * 3;
* });
* // => { 'a': 3, 'b': 6, 'c': 9 }
*/
function transform(object, iteratee, accumulator, thisArg) {
var isArr = isArray(object) || isTypedArray(object);
iteratee = baseCallback(iteratee, thisArg, 4);
if (accumulator == null) {
if (isArr || isObject(object)) {
var Ctor = object.constructor;
if (isArr) {
accumulator = isArray(object) ? new Ctor : [];
} else {
accumulator = baseCreate(typeof Ctor == 'function' && Ctor.prototype);
}
} else {
accumulator = {};
}
}
(isArr ? arrayEach : baseForOwn)(object, function(value, index, object) {
return iteratee(accumulator, value, index, object);
});
return accumulator;
}
return transform;
});