JavaScript filter through array of objects with a nested array and check for variable match within nested array

Question

I have an array of objects with one property being an array of values without keys and I am attempting to filter through and check for matching values within the nested array. Here is an example of one object:

[ 0:
    { fiber_phases: ["45", "46"],
      id: 1,
      label: "3200 to 3299 1 1/2 ST N",
      max_number: "3299",
      min_number: "3200",
      parsed_hash: "4028c7befc61ba4d07189f6ba99de35f",
      street: "1 1/2 ST N" 
    }
]

Here is my javascript code thus far:

return this.blocks
    .filter((block) => block.fiber_phases === fiberPhase)
    .map(({id, label, max_number, min_number, street, parsed_hash, fiber_phases}) => ({id: id, label: label, max_number: max_number, min_number: min_number, street: street, parsed_hash: parsed_hash, fiber_phases: fiber_phases}))

It's pretty clear that I'm not actually going into the nested array, but I haven't been able to access it.

I am attempting to filter through and check for matching values within the nested array. is definitely not clear. — void
– void, Commented Feb 27, 2018 at 19:01
I agree with @void, can you post an example of the input and desired output? — Rob M.
– Rob M., Commented Feb 27, 2018 at 19:02
Instead of block.fiber_phases === fiberPhase did you intend to do block.fiber_phases.includes(fiberPhase)? — trincot
– trincot, Commented Feb 27, 2018 at 19:03
I'll rephrase. My goal is to filter through an array of objects (all 11,231 of them), which each have a nested array of fiber_phases, and check for matches based on one fiberPhase value (i.e. let fiberPhase = '46'). I then would like to return a new array of objects that match that value. — Matt Larsuma
– Matt Larsuma, Commented Feb 27, 2018 at 19:03

T.J. Crowder · Accepted Answer · 2018-02-27 19:09:44Z

2

If you want to filter your main array such that it only contains objects that have fiberPhase anywhere in their fiber_phases array, you'd use filter with includes in the predicate:

return this.blocks.filter(block => block.fiber_phases.includes(fiberPhase));

Array.prototype.includes is relatively recent, but trivial to polyfill (see the link above). Or if you don't want to, indexOf will work:

return this.blocks.filter(block => block.fiber_phases.indexOf(fiberPhase) !== -1);

Note that that will return a new array which shares the objects with the original. If you wanted to copy them, you'd add

.map(entry => Object.assign({}, entry))

to it, or with some Stage 4 syntax that will be in the ES2018 spec:

.map(entry => ({...entry}))

Either way, it's a shallow copy (the fiber_phases array will be shared).

Adjust as needed.

edited Feb 27, 2018 at 19:09

answered Feb 27, 2018 at 19:04

T.J. Crowder

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4 Comments

T.J. Crowder Over a year ago

@MattLarson: FWIW, if you need to repeatedly filter the same array, and if you run into performance problems, it may be worth building a fiberPhase-to-array map once (with the attendant memory hit) which you can then reuse...

Matt Larsuma Over a year ago

Interesting. I'm also attempting to returning objects that contain a value match in the nested array and no other values :/ So right now, .filter((block) => block.fiber_phases.includes(fiberPhase)) will return results sets that match fiberPhase and ones that match other fiberPhases as well. If only there was an .onlyIncludes() hah

T.J. Crowder Over a year ago

@MattLarson: Wouldn't that be block => block.fiber_phases.length == 1 && block.fiber_phases[0] == fiberPhase ? :-)

Matt Larsuma Over a year ago

I think that'd work! I'm having another issue, so I'll check in a moment.

trincot · Accepted Answer · 2018-02-27 19:05:57Z

1

You can achieve that with includes and Object.assign:

return this.blocks
    .filter(block => block.fiber_phases.include(fiberPhase))
    .map(block => Object.assign({}, block));

Or with the more recent ECMAScript 2018 spread syntax for object literals:

return this.blocks
    .filter(block => block.fiber_phases.include(fiberPhase))
    .map(block => ({...block}));

answered Feb 27, 2018 at 19:05

trincot

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