Cookbook

This page contains a collection of 'recipes', simple examples of partial.lenses-based solutions to common problems.

Isomorphic Conversion between an Array of Objects and a Single Object

• Convert a structure like this [ { id: 'a', v: 1 }, { id: 'b', v: 2 } ]
• To one like this { a: 1, b: 2 } (and back).
• See it in action on the partial.lenses Playground.

const data = [ { id: 'a', val: 1 }, { id: 'b', val: 2 } ]

const arrayToObjectL = ( keyProp, valProp ) => xs =>
  xs.reduce( ( acc, x ) => ( acc[ x[ keyProp ] ] = x[ valProp ], acc ), {} )

const objectToArrayL = ( keyProp, valProp ) => obj =>
  Object.keys( obj ).map( x => ( { [ keyProp ]: x, [ valProp ]: obj[ x ] } ) )

const arrayToObjectIsoL = ( keyProp, valProp ) =>
  L.iso( arrayToObjectL( keyProp, valProp ), objectToArrayL( keyProp, valProp ) )

const d1 = L.get( arrayToObjectIsoL( 'id', 'val' ), data )
const d2 = L.modify( [ arrayToObjectIsoL( 'id', 'val' ), L.values ], R.inc, data )

R.identity( { d1, d2 } )

// result:
{
  "d1": { "a": 1, "b": 2 },
  "d2": [ { "id": "a", "val": 2 }, { "id": "b" "val": 3 } ]
}