使用Ramda对数组的项进行分组和变换

Question

I need to group items from an array by batchNumber and sum their values.

Currently I am using ramda, but I am able to group but not to transform the result.

Could you please provide me an example using ramda.js?

Live Example :

const input = [
    {
        batchNumber: 'a',
        scrapAmount: 5
    },
    {
        batchNumber: 'a',
        scrapAmount: 10
    },
    {
        batchNumber: 'b',
        scrapAmount: 1
    },
    {
        batchNumber: 'b',
        scrapAmount: 2
    },
    {
        scrapAmount: 7
    },
    {
        scrapAmount: 3
    }
]

const byBatchNumber = R.groupBy((batch) => batch.batchNumber);


console.log(byBatchNumber(input))

/* result wanted

const output = [
    {
        batchNumber: 'a',
        scrapAmount: 15
    },
    {
        batchNumber: 'b',
        scrapAmount: 3
    },
    {
        batchNumber: undefined,
        scrapAmount: 10
    },
]

*/

Answer 1

You groupWith() by checking that the batchNumber is equal with eqProps() . Then map() each subarray, apply mergeWithKey() to all objects, and add() the values of the scrapAmount field:

 const { compose, groupWith, eqProps, map, apply, mergeWithKey, add } = R; const input = [{"batchNumber":"a","scrapAmount":5},{"batchNumber":"a","scrapAmount":10},{"batchNumber":"b","scrapAmount":1},{"batchNumber":"b","scrapAmount":2},{"scrapAmount":7},{"scrapAmount":3}] const byBatchNumber = compose( map(apply(mergeWithKey((k, l, r) => k === 'scrapAmount' ? add(l, r) : r))), groupWith(eqProps('batchNumber')) ) console.log(byBatchNumber(input)) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script> 

Answer 2

A fairly simple version would be the following:

 const {pipe, groupBy, prop, map, pluck, sum} = R; const input = [ {batchNumber: 'a', scrapAmount: 5}, {batchNumber: 'a', scrapAmount: 10}, {batchNumber: 'b', scrapAmount: 1}, {batchNumber: 'b', scrapAmount: 2}, {scrapAmount: 7}, {scrapAmount: 3} ] const totalScrap = pipe( groupBy(prop('batchNumber')), map(pluck('scrapAmount')), map(sum) ) console.log(totalScrap(input)) 

 <script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script> 

Note first that this simplifies R.groupBy((batch) => batch.batchNumber) to R.groupBy(R.prop('batchNumber')) ; it' the same functionality, just expressed more concisely.

This is as far as I would go, because I believe this to be the most helpful output format for the work I usually do, namely something like this:

{"a": 15, "b": 3, "undefined": 10}

But rereading your required output, it might take two more steps:

 const {pipe, groupBy, prop, map, pluck, sum, toPairs, zipObj} = R; const input = [ {batchNumber: 'a', scrapAmount: 5}, {batchNumber: 'a', scrapAmount: 10}, {batchNumber: 'b', scrapAmount: 1}, {batchNumber: 'b', scrapAmount: 2}, {scrapAmount: 7}, {scrapAmount: 3} ] const totalScrap = pipe( groupBy(prop('batchNumber')), map(pluck('scrapAmount')), map(sum), toPairs, map(zipObj(['batchNumber', 'scrapAmount'])) ) console.log(totalScrap(input)) 

 <script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script> 

One thing this doesn't do is to generate an item with batchNumber: undefined , and instead returns one with batchNumber: "undefined" (a string.) While this could be fixed, it's an ugly step, and I don't see a real gain. And likely solutions would then fail if you had one with a value of "undefined" . If this is really a show-stopper, you could obviously process these before the last step in that pipeline.