CODEWITHSUNDEEP
javascriptfunctional-programmingramda.js
Evan Carroll
Evan Carroll

Reputation: 1

Javascript iterate over two-elements in a list when not concerned about result?

Let's say I have a list like

let chain = [ 1, 9, 61, 798 ];

These are essentially denormalized nodes on a route, and I want to add the edges in a database. Ideally I'm looking for something that calls addEdge(node,parent) for each two elements in the list. I'm looking for the Ramda way of doing this.

Does it bring any unique ability to the mix? I've thought of using something like .reduceRight() from core javascript,

[ 1, 9, 61, 798 ].reduceRight( (acc,v) => {
  addEdge(acc,v);
  return v
}, undefined );

But in this case, .reduceRight is returning something and seems weird to use that in void-context. Is there a better way to do this?

Upvotes: 1

Views: 93

Answers (2)

Matías Fidemraizer
Matías Fidemraizer

Reputation: 64943

Here's a vanilla JavaScript approach:

const range = (from, to) => {
  const output = []

  for (let i = from; i < to; i++)
    output.push (i)

  return output
}

const pairize = xs =>
  range (0, xs.length - 1)
  .map (i => [xs[i], xs[i + 1]])


const nodes = [1, 9, 61, 798]
const edges = pairize (nodes)

console.log (edges)

Upvotes: 0

Scott Christopher
Scott Christopher

Reputation: 6516

You can use R.aperture to produce a new array containing consecutive elements of a given size.

const nodes = [1, 9, 61, 798]
const edges = R.aperture(2, nodes)

console.log(edges) //=> [[1, 9], [9, 61], [61, 798]]
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.min.js"></script>

You can then either map or forEach over the resulting array containing the pairs of nodes.

Upvotes: 3

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