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'use strict'; |
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Object.defineProperty(exports, "__esModule", { |
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value: true |
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}); |
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exports.default = reduce; |
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|
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var _eachOfSeries = require('./eachOfSeries'); |
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var _eachOfSeries2 = _interopRequireDefault(_eachOfSeries); |
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var _noop = require('lodash/noop'); |
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var _noop2 = _interopRequireDefault(_noop); |
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var _once = require('./internal/once'); |
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var _once2 = _interopRequireDefault(_once); |
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var _wrapAsync = require('./internal/wrapAsync'); |
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var _wrapAsync2 = _interopRequireDefault(_wrapAsync); |
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|
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function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; } |
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|
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/** |
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* Reduces `coll` into a single value using an async `iteratee` to return each |
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* successive step. `memo` is the initial state of the reduction. This function |
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* only operates in series. |
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* |
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* For performance reasons, it may make sense to split a call to this function |
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* into a parallel map, and then use the normal `Array.prototype.reduce` on the |
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* results. This function is for situations where each step in the reduction |
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* needs to be async; if you can get the data before reducing it, then it's |
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* probably a good idea to do so. |
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* |
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* @name reduce |
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* @static |
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* @memberOf module:Collections |
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* @method |
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* @alias inject |
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* @alias foldl |
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* @category Collection |
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* @param {Array|Iterable|Object} coll - A collection to iterate over. |
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* @param {*} memo - The initial state of the reduction. |
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* @param {AsyncFunction} iteratee - A function applied to each item in the |
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* array to produce the next step in the reduction. |
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* The `iteratee` should complete with the next state of the reduction. |
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* If the iteratee complete with an error, the reduction is stopped and the |
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* main `callback` is immediately called with the error. |
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* Invoked with (memo, item, callback). |
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* @param {Function} [callback] - A callback which is called after all the |
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* `iteratee` functions have finished. Result is the reduced value. Invoked with |
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* (err, result). |
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* @example |
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* |
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* async.reduce([1,2,3], 0, function(memo, item, callback) { |
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* // pointless async: |
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* process.nextTick(function() { |
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* callback(null, memo + item) |
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* }); |
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* }, function(err, result) { |
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* // result is now equal to the last value of memo, which is 6 |
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* }); |
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*/ |
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function reduce(coll, memo, iteratee, callback) { |
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callback = (0, _once2.default)(callback || _noop2.default); |
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var _iteratee = (0, _wrapAsync2.default)(iteratee); |
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(0, _eachOfSeries2.default)(coll, function (x, i, callback) { |
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_iteratee(memo, x, function (err, v) { |
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memo = v; |
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callback(err); |
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}); |
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}, function (err) { |
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callback(err, memo); |
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}); |
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} |
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module.exports = exports['default']; |
