Может кто-нибудь написать такую функцию на Си++?
/**
* Group items by field
*
* items =
* [{id: 1, name: 'A', i: 1}, {id: 2, name: 'B', i: 2}, {id: 3, name: 'A', i: 3}, {id: 4, name: 'B', i: 4}, {id: 5, name: 'A', i: 5}]
*
* groupByField(items, 'name', ['i']) =
* [
* {
* groupField: 'name',
* groupValue: 'A',
* items: [{id: 1, name: 'A', i: 1}, {id: 3, name: 'A', i: 3}, {id: 5, name: 'A', i: 5}],
* id: 1, //First value
* i: 9 //Summed value
* }, {
* groupField: 'name',
* groupValue: 'B',
* items: [{id: 2, name: 'B', i: 2}, {id: 4, name: 'B', i: 4}],
* id: 2,
* i: 6
* }
* ]
*
*
@param items - Array<any> - items array
*
@param field - string - field name
*
@param sumFields - Array<string> - array with names of fields which should be summed
*
@returns Array<any>
*/
function groupByField(items, field, sumFields = []) {
const itemsByField = new Map() // We need correct order of items
const sumReducer = (fieldName) => (prev, next) => (prev + next[fieldName] || 0);
const result = [];
for (let i = 0; i < items.length; i++) {
const item = items[i];
const groupKey = item[field];
const groupedCollection = itemsByField.get(groupKey) || [];
if (!groupedCollection.length) {
itemsByField.set(groupKey, groupedCollection);
}
groupedCollection.push(item);
}
for (const entry of itemsByField) {
const key = entry[0];
const items = entry[1];
const aggregatedItem = { ...items[0] }; // Copy first item
// Calculate values which should be summed
for (let j = 0; j < sumFields.length; j++) {
const fieldName = sumFields[j];
aggregatedItem[fieldName] = items.reduce(sumReducer(fieldName), 0)
}
aggregatedItem.groupField = field;
aggregatedItem.groupValue = key;
aggregatedItem.items = items;
result.push(aggregatedItem);
}
return result;
}
