Change object attribute in an array of objects with Ramda.js

Create a Map of statuses and their replacements, and a function to return the replacement (updateStatus) when given a value (current). Iterate the array with R.map, and use R.evolve to create a new object with updated status.

const status = new Map([['emitted', 'done'], ['changed', 'error']])

// get the current state replacement from the Map or use current if no replacement is available
const updateStatus = current => status.get(current) || current

const fn = R.map(R.evolve({
  attributes: {
    status: updateStatus
  }
}))

const data = [{type: 'x', 'attributes': {status: 'emitted', num: 1}}, { type: 'y', attributes: {status: 'changed', num: 2}}]

const result = fn(data)

console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>

To fully appreciate the API ramda provides, I think it's worth it to add the "plain" javascript alternative (If you're willing to use the ECMAScript 2018 Object Spread syntax).

In the function arguments, you destructure your object right up until the properties you'd like to modify. All others props are collected in a ...rest parameter.

In the body of the map function, you recreate a new object, making the modifications to the properties you need.

As you can see, it can be quite hard to parse out the parts that are being changed. +1 to the ramda approach 🙂

const entries = [ { type: 'x', 'attributes': {status: 'emitted', num: 1}}, { type: 'y', attributes: {status: 'changed', num: 2 } } ];

const statusMap = { "emitted": "done", "changed": "error" };

console.log(
  entries.map(
    ({ attributes: { status, ...ra }, ...re }) =>
    ({ attributes: { status: statusMap[status], ...ra }, ...re })
  )
);

import { lensPath, map, over } from 'ramda'

const status = {emitted: 'done', changed: 'error'}
const updateStatus = current => status[current] ?? current
const statusLens = lensPath(['attributes', 'status']) 
const updateStatus = map(over(statusLens, updateStatus))

updateStatus([
  {type: 'x', 'attributes': {status: 'emitted', num: 1}}, 
  {type: 'y', attributes: {status: 'changed', num: 2}}
])
// =>
// [
//   {type: 'x', 'attributes': {status: 'done', num: 1}}, 
//   {type: 'y', attributes: {status: 'error', num: 2}}
// ]