Change array list into multiple array lists every 3 items

Question

I want to filter a large array list into multiple arrays for every 5 items in a certain way so that [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] would be [[1, 2, [3, 4, 5]], [6, 7, [8, 9, 10]]] or [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15] would be [[1, 2, [3, 4, 5]], [6, 7, [8, 9, 10]], [11, 12, [13, 14, 15]]]. (All arrays will be a multiple of 5 in my program.)

How would I do this?

Right now I'm doing this

for (var i = 1; i < (stoneTextureUnfiltered.length+1)/1.01; i++) {
    stoneTexture.push([stoneTextureUnfiltered[i], stoneTextureUnfiltered[i+1], stoneTextureUnfiltered[i+2], [stoneTextureUnfiltered[i+3], stoneTextureUnfiltered[i+4], stoneTextureUnfiltered[i+5]]]);
}

but it doesn't seem to be working.

Thanks,

-Voxel

What would 1-11 output? what about 7-19? Please give examples of other inputs and outputs? — evolutionxbox
– evolutionxbox, Commented May 4, 2022 at 13:56
You can chunk the array into 5's with this question, then for each chunk, wrap the last 3 in another array. — k.tten
– k.tten, Commented May 4, 2022 at 14:01
I discontinued Processing.js in December of 2018. You should not be using it for new projects (instead, give p5js a try. Especially given the legacy JS you're showing: we no longer use var because it's really weirdly scoped. Either use const for variables that should not get reassigned, or let if you need to reassign values to it) — Mike 'Pomax' Kamermans
– Mike 'Pomax' Kamermans, Commented May 11, 2022 at 0:47

k.tten · Accepted Answer · 2022-05-04 14:03:11Z

0

Assuming you've chunked the array already into parts of 5 with these answers and it's stored in a variable named chunks, to wrap the last 3 in each chunk you can use map:

const final = chunks.map((chunk) => [chunk[0], chunk[1], chunk.slice(2)]);

You add the first and second elements to the new list, then add the rest of the chunk as a whole.

Demo below:

// using second answer
var perChunk = 5 // items per chunk    

var inputArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

var chunks = inputArray.reduce((resultArray, item, index) => { 
  const chunkIndex = Math.floor(index/perChunk)

  if(!resultArray[chunkIndex]) {
    resultArray[chunkIndex] = [] // start a new chunk
  }

  resultArray[chunkIndex].push(item)

  return resultArray
}, [])

// answer below

const final = chunks.map((chunk) => [chunk[0], chunk[1], chunk.slice(2)]);

console.log(final);

As you can see, it works nicely!

answered May 4, 2022 at 14:03

k.tten

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8 Comments

Voxel Over a year ago

Unfortunately, the program I'm using doesn't support ES6. It's really annoying, but is there a way I can do this without ES6 syntax (such as =>)?

k.tten Over a year ago

That shouldn't matter. If you read the first answer in the question I linked the answer uses simple traditional loops.

Voxel Over a year ago

const final = chunks.map((chunk) => [chunk[0], chunk[1], chunk.slice(2)]); uses ES6 syntax (const and =>), which the program I'm using doesn't support. What do you mean it "shouldn't matter"?

k.tten Over a year ago

You can convert that to var final = chunks.map(function mapper(chunk) { return [chunk[0], chunk[1], chunk.slice(2)]; });, which does not rely on any ES6 features.

Voxel Over a year ago

Still refuses to work. I did this and it gave me the error "[object Array] is not a function".

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