jiapengyu
58 lines
2.3 KiB
JavaScript
58 lines
2.3 KiB
JavaScript
import _curryN from './internal/_curryN';
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import _dispatchable from './internal/_dispatchable';
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import _has from './internal/_has';
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import _reduce from './internal/_reduce';
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import _xreduceBy from './internal/_xreduceBy';
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/**
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* Groups the elements of the list according to the result of calling
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* the String-returning function `keyFn` on each element and reduces the elements
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* of each group to a single value via the reducer function `valueFn`.
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*
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* This function is basically a more general [`groupBy`](#groupBy) function.
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*
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* Acts as a transducer if a transformer is given in list position.
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*
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* @func
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* @memberOf R
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* @since v0.20.0
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* @category List
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* @sig ((a, b) -> a) -> a -> (b -> String) -> [b] -> {String: a}
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* @param {Function} valueFn The function that reduces the elements of each group to a single
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* value. Receives two values, accumulator for a particular group and the current element.
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* @param {*} acc The (initial) accumulator value for each group.
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* @param {Function} keyFn The function that maps the list's element into a key.
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* @param {Array} list The array to group.
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* @return {Object} An object with the output of `keyFn` for keys, mapped to the output of
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* `valueFn` for elements which produced that key when passed to `keyFn`.
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* @see R.groupBy, R.reduce
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* @example
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*
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* var reduceToNamesBy = R.reduceBy((acc, student) => acc.concat(student.name), []);
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* var namesByGrade = reduceToNamesBy(function(student) {
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* var score = student.score;
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* return score < 65 ? 'F' :
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* score < 70 ? 'D' :
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* score < 80 ? 'C' :
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* score < 90 ? 'B' : 'A';
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* });
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* var students = [{name: 'Lucy', score: 92},
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* {name: 'Drew', score: 85},
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* // ...
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* {name: 'Bart', score: 62}];
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* namesByGrade(students);
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* // {
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* // 'A': ['Lucy'],
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* // 'B': ['Drew']
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* // // ...,
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* // 'F': ['Bart']
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* // }
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*/
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var reduceBy = /*#__PURE__*/_curryN(4, [], /*#__PURE__*/_dispatchable([], _xreduceBy, function reduceBy(valueFn, valueAcc, keyFn, list) {
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return _reduce(function (acc, elt) {
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var key = keyFn(elt);
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acc[key] = valueFn(_has(key, acc) ? acc[key] : valueAcc, elt);
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return acc;
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}, {}, list);
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}));
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export default reduceBy; |