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import arrayMap from 'lodash/_arrayMap';
import property from 'lodash/_baseProperty';
import map from './map';
/**
* Sorts a list by the results of running each `coll` value through an async
* `iteratee`.
*
* @name sortBy
* @static
* @memberOf module:Collections
* @method
* @category Collection
* @param {Array|Iterable|Object} coll - A collection to iterate over.
* @param {Function} iteratee - A function to apply to each item in `coll`.
* The iteratee is passed a `callback(err, sortValue)` which must be called once
* it has completed with an error (which can be `null`) and a value to use as
* the sort criteria. Invoked with (item, callback).
* @param {Function} callback - A callback which is called after all the
* `iteratee` functions have finished, or an error occurs. Results is the items
* from the original `coll` sorted by the values returned by the `iteratee`
* calls. Invoked with (err, results).
* @example
*
* async.sortBy(['file1','file2','file3'], function(file, callback) {
* fs.stat(file, function(err, stats) {
* callback(err, stats.mtime);
* });
* }, function(err, results) {
* // results is now the original array of files sorted by
* // modified date
* });
*
* // By modifying the callback parameter the
* // sorting order can be influenced:
*
* // ascending order
* async.sortBy([1,9,3,5], function(x, callback) {
* callback(null, x);
* }, function(err,result) {
* // result callback
* });
*
* // descending order
* async.sortBy([1,9,3,5], function(x, callback) {
* callback(null, x*-1); //<- x*-1 instead of x, turns the order around
* }, function(err,result) {
* // result callback
* });
*/
export default function sortBy (coll, iteratee, callback) {
map(coll, function (x, callback) {
iteratee(x, function (err, criteria) {
if (err) return callback(err);
callback(null, {value: x, criteria: criteria});
});
}, function (err, results) {
if (err) return callback(err);
callback(null, arrayMap(results.sort(comparator), property('value')));
});
function comparator(left, right) {
var a = left.criteria, b = right.criteria;
return a < b ? -1 : a > b ? 1 : 0;
}
}
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