How to map an array of objects to a single object using Ramda

Question

I need to turn this:

let arr = [{ id: 1, name: 'rod'} , { id: 2, name: 'hey' }]

into:

mapO = { 1: 'rod', 2: 'hey' }

That's what I tried:

let mapIdName = (o) => {
  let ret = {};
  ret[o["id"]] = o['name'];
  return ret;
}

let mergeIdNames = R.mergeAll(R.map(mapIdName));

mergeIdNames(o)

with the error:

mergeIdNames is not a function

Answer 1

You could use R.indexBy :

> R.map(R.prop('name'), R.indexBy(R.prop('id'), [{id: 1, name: 'rod'}, {id: 2, name: 'hey'}]))
{'1': 'rod', '2': 'hey'}

As a function:

//    f :: Array { id :: String, name :: a } -> StrMap a
const f = R.pipe(R.indexBy(R.prop('id')), R.map(R.prop('name')));

f([{id: 1, name: 'rod'}, {id: 2, name: 'hey'}]);
// => {'1': 'rod', '2': 'hey'}

Answer 2

Even using Reduce leads to a fairly terse and readable code:

reduce((acc, curr) => 
   R.assoc(curr.id, curr.name, acc), {}, arr)

Or if used as a function:

const f = R.reduce((acc, curr) => 
   R.assoc(curr.id, curr.name, acc), {})