lodash groupby 和 sum 对象属性

Question

I have an array of Objects that I need to reduce down based on a property and sum the other property. This solution is pretty much what I'm after , but I need to avoid using _.chain as am importing only specific modules.

I've tried using flow, but am not getting any values:

const sumBy = require('lodash/fp/sumBy');
const flow = require('lodash/fp/flow');
const groupBy = require('lodash/fp/groupBy');
const map = require('lodash/fp/map');

const list = [
    { property: 'foo', value: 1 },
    { property: 'foo', value: 3 },
    { property: 'bar', value: 2 },
    { property: 'bar', value: 3 },
    { property: 'chu', value: 8 },
];

const foo = flow(
  groupBy('property'),
  map((objs, key) => {
    return {
      property: key,
      value: sumBy(objs, 'value')
    }
  })
)(list)

This returns

[
    { property: undefined, value: 0 },
    { property: undefined, value: 0 },
    { property: undefined, value: 0 }
]

Ideally, I'd like to do this in vanilla es6, I've had a go at it, but not sure how to do the sum.

const bar = list.reduce((o, v) => {
    return {...o, [v.property]: v.value}
}, {})

Answer 1

How about the following ES6 only solution:

 const list = [ { property: 'foo', value: 1 }, { property: 'foo', value: 3 }, { property: 'bar', value: 2 }, { property: 'bar', value: 3 }, { property: 'chu', value: 8 }, ]; const result = list.reduce((obj, el) => { obj[el.property] = (obj[el.property] || 0) + el.value; return obj; }, {}); console.log(result);

Answer 2

You could take a Map .

 const list = [{ property: 'foo', value: 1 }, { property: 'foo', value: 3 }, { property: 'bar', value: 2 }, { property: 'bar', value: 3 }, { property: 'chu', value: 8 }], result = Array.from( list.reduce((m, { property, value }) => m.set(property, (m.get(property) || 0) + value), new Map), (([property, value]) => ({ property, value })) ); console.log(result);

 .as-console-wrapper { max-height: 100% !important; top: 0; }

With lodash

 const list = [{ property: 'foo', value: 1 }, { property: 'foo', value: 3 }, { property: 'bar', value: 2 }, { property: 'bar', value: 3 }, { property: 'chu', value: 8 }], result = _(list) .groupBy('property') .map((array, property) => ({ property, value: _.sumBy(array, 'value')})) ; console.log(result);

 .as-console-wrapper { max-height: 100% !important; top: 0; }

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>

Answer 3

This could be thought of as a less efficient but nicer-to-read variant of the answer from Ruben Helsloot.

 const sumValues = list => list .reduce ((obj, {property, value}) => ({ ... obj, [property]: (obj [property] || 0) + value }), {}) const list = [{property: 'foo', value: 1}, {property: 'foo', value: 3}, {property: 'bar', value: 2}, {property: 'bar', value: 3}, {property: 'chu', value: 8}] console .log (sumValues (list))