Move items to front of array if they exists in another array, based on key

Question

I'm sort an array based on the keys in another array. If they find a match, it would move those items to the front of the array. But I can't think of a clean way to do this.

let myArray = [
  { id: 'a', name: 'Mal' },
  { id: 'b', name: 'Wash'},
  { id: 'c', name: 'Inara'},
  { id: 'd', name: 'Jayne'},
  ]

let sortArray = [
  { id: 'b' },
  { id: 'c' },
  { id: 'x' },
]

/* Expected result
myArray = [
  { id: 'b', name: 'Wash'},
  { id: 'c', name: 'Inara'},
  { id: 'a', name: 'Mal' },
  { id: 'd', name: 'Jayne'},
  ]
/*

Does anyone know a way to do this without just looping through it a bunch of times? Thanks

adiga · Accepted Answer · 2020-10-12 12:32:02Z

2

You could create a Map which maps each id in sortArray to its index. Use this priority map object to sort the first array.

const array = [{ id: 'a', name: 'Mal' }, { id: 'b', name: 'Wash'}, { id: 'c', name: 'Inara'}, { id: 'd', name: 'Jayne'}],
     sortArray = [{ id: 'b' }, { id: 'c' }, { id: 'x' }],
     map = new Map( sortArray.map((o, i) => [o.id, i]) )

array.sort((a,b) => 
  ( map.has(b.id) - map.has(a.id) ) || ( map.get(a.id) - map.get(b.id) )
)

console.log(array)

answered Oct 12, 2020 at 12:32

adiga

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Nina Scholz · Accepted Answer · 2020-10-12 12:25:41Z

1

You could take an object ffor the wanted order of the items and a default value for unknown items.

let array = [{ id: 'a', name: 'Mal' }, { id: 'b', name: 'Wash'}, { id: 'c', name: 'Inara'}, { id: 'd', name: 'Jayne'}],
    sortArray = [{ id: 'b' }, { id: 'c' }, { id: 'x' }],
    order = Object.fromEntries(sortArray.map(({ id }, i) => [id, i + 1]));

array.sort(({ id: a }, { id: b }) =>
    (order[a] || Number.MAX_VALUE) - (order[b] || Number.MAX_VALUE)
);

console.log(array);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Oct 12, 2020 at 12:25

Nina Scholz

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