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import noop from './internal/noop';
import mapLimit from './mapLimit';
import wrapAsync from './internal/wrapAsync';
/**
* The same as [`groupBy`]{@link module:Collections.groupBy} but runs a maximum of `limit` async operations at a time.
*
* @name groupByLimit
* @static
* @memberOf module:Collections
* @method
* @see [async.groupBy]{@link module:Collections.groupBy}
* @category Collection
* @param {Array|Iterable|Object} coll - A collection to iterate over.
* @param {number} limit - The maximum number of async operations at a time.
* @param {AsyncFunction} iteratee - An async function to apply to each item in
* `coll`.
* The iteratee should complete with a `key` to group the value under.
* Invoked with (value, callback).
* @param {Function} [callback] - A callback which is called when all `iteratee`
* functions have finished, or an error occurs. Result is an `Object` whoses
* properties are arrays of values which returned the corresponding key.
*/
export default function(coll, limit, iteratee, callback) {
callback = callback || noop;
var _iteratee = wrapAsync(iteratee);
mapLimit(coll, limit, (val, iterCb) => {
_iteratee(val, (err, key) => {
if (err) return iterCb(err);
return iterCb(null, {key, val});
});
}, (err, mapResults) => {
var result = {};
// from MDN, handle object having an `hasOwnProperty` prop
var {hasOwnProperty} = Object.prototype;
for (var i = 0; i < mapResults.length; i++) {
if (mapResults[i]) {
var {key} = mapResults[i];
var {val} = mapResults[i];
if (hasOwnProperty.call(result, key)) {
result[key].push(val);
} else {
result[key] = [val];
}
}
}
return callback(err, result);
});
}
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