Dynamically build expression to filter Javascript array

Question

I need to filter an array based an a variable number of items in another array. Say my array to be filtered looks like this :

var toBeFiltered = [
  {name:"A", parentId: 0},
  {name: "B", parentId: 3},
  {name: "C", parentId: 0},
  {name: "D", parentId: 1},
  ...
]

I need to filter all the elements for which parentId is in another array (say : var filtering = [3,1,0], but it can have any length). How can I build a filter expression dynamically based on the content of the filtering array ? In this case I'd end up with this expression :

function(d){return d.parentId == 3 || d.parentId == 1 || d.parentId == 0;}

Is there any smart way to do this ? Something like concatenation of boolean expressions ?

Mihai Alexandru-Ionut · Accepted Answer · 2017-10-11 14:15:21Z

5

You can use indexOf method which checks if an item exists in a given array.

indexOf method returns first occurrence of the specified value and returns -1 if the value is not found.

var toBeFiltered = [
  {name:"A", parentId: 0},
  {name: "B", parentId: 3},
  {name: "C", parentId: 0},
  {name: "D", parentId: 1},
  {name: "E", parentId: 4}
]
var filtering = [3,1,0];
toBeFiltered=toBeFiltered.filter(a=>filtering.indexOf(a.parentId)!==-1);
console.log(toBeFiltered);

Also you can use Set feature from ES6.

var toBeFiltered = [
  {name:"A", parentId: 0},
  {name: "B", parentId: 3},
  {name: "C", parentId: 0},
  {name: "D", parentId: 1},
  {name: "E", parentId: 4}
]
var filtering = new Set([3,1,0]);
toBeFiltered=toBeFiltered.filter(a=>filtering.has(a.parentId));
console.log(toBeFiltered);

edited Oct 11, 2017 at 14:15

answered Oct 11, 2017 at 14:09

Mihai Alexandru-Ionut

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1 Comment

GuitarExtended Over a year ago

Simple and elegant. I hadn't thought about this. Thanks.

Nina Scholz · Accepted Answer · 2017-10-11 14:11:01Z

3

You could take Array#includes

var toBeFiltered = [{ name:"A", parentId: 0 }, { name: "B", parentId: 3 }, { name: "C", parentId: 0 }, { name: "D", parentId: 1 }],
    filtering = [1, 0], // to prevent to get the same array as the original
    result = toBeFiltered.filter(o => filtering.includes(o.parentId));
    
console.log(result);

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answered Oct 11, 2017 at 14:11

Nina Scholz

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1 Comment

GuitarExtended Over a year ago

Thank you. I accepted the other answer because includes is less supported than indexOf.

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