How to get two arrays by mapping a predicate over an input array with Ramda

Question

Is there a concise way to achieve the same result as the below but:

• without mutation
• without iterating over the input array more than once
• using Ramda (preferably)

I thought about using reduce to update an accumulator object containing the passed/failed arrays, but I'm not sure if there was a smarter/less verbose option

const predicate = i => i % 2 === 0;
const predicatePassed = [];
const predicateFailed = [];

[1, 2, 3, 4].forEach(i => predicate(i) ? predicatePassed.push(i) : predicateFailed.push(i))

// predicatePassed === [2, 4]
// predicateFailed === [1, 3]

Answer 1

You can use R.partition :

 const predicate = i => i % 2 === 0; const [predicatePassed, predicateFailed] = R.partition(predicate)([1, 2, 3, 4]); console.log(predicatePassed); console.log(predicateFailed); 

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