groupBy.js•1.74 kB
var _curry2 = require('./internal/_curry2');
var _dispatchable = require('./internal/_dispatchable');
var _xgroupBy = require('./internal/_xgroupBy');
var reduceBy = require('./reduceBy');
/**
* Splits a list into sub-lists stored in an object, based on the result of
* calling a String-returning function on each element, and grouping the
* results according to values returned.
*
* Dispatches to the `groupBy` method of the second argument, if present.
*
* Acts as a transducer if a transformer is given in list position.
*
* @func
* @memberOf R
* @since v0.1.0
* @category List
* @sig (a -> String) -> [a] -> {String: [a]}
* @param {Function} fn Function :: a -> String
* @param {Array} list The array to group
* @return {Object} An object with the output of `fn` for keys, mapped to arrays of elements
* that produced that key when passed to `fn`.
* @see R.transduce
* @example
*
* var byGrade = R.groupBy(function(student) {
* var score = student.score;
* return score < 65 ? 'F' :
* score < 70 ? 'D' :
* score < 80 ? 'C' :
* score < 90 ? 'B' : 'A';
* });
* var students = [{name: 'Abby', score: 84},
* {name: 'Eddy', score: 58},
* // ...
* {name: 'Jack', score: 69}];
* byGrade(students);
* // {
* // 'A': [{name: 'Dianne', score: 99}],
* // 'B': [{name: 'Abby', score: 84}]
* // // ...,
* // 'F': [{name: 'Eddy', score: 58}]
* // }
*/
module.exports = _curry2(_dispatchable('groupBy', _xgroupBy, reduceBy(function(acc, item) {
if (acc == null) {
acc = [];
}
acc.push(item);
return acc;
}, null)));