[removed] Make an array of value pairs form an array of values

Question

Is there an elegant, functional way to turn this array:

[ 1, 5, 9, 21 ]

into this

[ [1, 5], [5, 9], [9, 21] ]

I kn

Answer 1

You could map a spliced array and check the index. If it is not zero, take the predecessor, otherwise the first element of the original array.

var array = [1, 5, 9, 21],
    result = array.slice(1).map((a, i, aa) => [i ? aa[i - 1] : array[0], a]);

console.log(result);

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An even shorter version, as suggested by Bergi:

var array = [1, 5, 9, 21],
    result = array.slice(1).map((a, i) => [array[i], a]);

console.log(result);

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