To use modern array methods to generate 2 dimensional array

Question

How to filter out an array in such a way that the empty indexes should trigger a new array and the result becomes a two dimensional array. Tried with Vanilla JavaScript and it works, looking for a solution using modern array methods.

var list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""];

Vanilla JavaScript eg:-

var tmp_list = [];
    for(let i=0; i<list.length; i++) {
        if(list[i].length > 0) {
          tmp_list.push(list[i]);
        } else {
          result_array.push(tmp_list);
          tmp_list = [];
        }
    }

for eg:-

Array indexes with values should be consolidated into an array which is then pushed to the result array

Expected result

var result_array = [["1", "2", "3"], ["4", "5", "6"], ["7", "8", "9"]];

zer00ne · Accepted Answer · 2022-12-11 18:26:00Z

2

Details are commented in example

const list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""];

const result = list.reduce((sub, cur, idx, arr) => {
  /*
  If current value is a "" AND current index is NOT the last index
  add an empty array at the end of array "sub"
  */
  if (cur === "" && idx !== arr.length - 1) {
    sub.push([]);
  /* 
  Otherwise if current value is "truthy" (not a "")
  add current value to the last sub-array of "sub"
  */
  } else if (cur) {
    sub[sub.length - 1].push(cur);
  }
  return sub;
}, [[]]);// Initial "sub" is an empty array of arrays

console.log(result);

answered Dec 11, 2022 at 18:26

zer00ne

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Comments

Amirhossein · Accepted Answer · 2022-12-11 18:19:25Z

1

Hope it helps:

var list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""];
const result = [];
let spaceIndex = list.indexOf("");
while(spaceIndex !== -1) {
  result.push(list.slice(0, spaceIndex));
  list = list.slice(spaceIndex + 1);
  spaceIndex = list.indexOf("");
}
console.log(result);

answered Dec 11, 2022 at 18:19

Amirhossein

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1 Comment

Peter Seliger Over a year ago

@coloraddict ... Having a late look into this thread again it somehow cheers me up that despite the question ... "To use modern array methods to generate 2 dimensional array" ... the accepted answer is almost the only one which uses additional variables in the outer scope due to an outer while based approach (thus not processing list directly by an array method like shown with Nina's or zer00ne's reduce).

Nina Scholz · Accepted Answer · 2022-12-11 18:07:06Z

1

You could reduce the array and look for undefined or a falsy value like '' and push a new array to the result set.

const
    list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""],
    result = list.reduce((r, v, i, a) => {
        if (!a[i - 1]) r.push([]);
        if (v) r.at(-1).push(v);
        return r;
    }, []);

console.log(result);

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

answered Dec 11, 2022 at 18:07

Nina Scholz

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Comments

Heiko Jakubzik · Accepted Answer · 2022-12-11 18:09:20Z

1

const list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""];
var result_array = [];
var tmp_list = [];
list.forEach( item => {
    if( item === "" ) { result_array.push( tmp_list ); tmp_list = []; }
    else tmp_list.push( item );
});

console.log( result_array );

@Nina Scholz is more elegant -- this seems more readable to me, though.

answered Dec 11, 2022 at 18:09

Heiko Jakubzik

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Comments

Andrew Parks · Accepted Answer · 2022-12-11 18:59:12Z

1

const list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""];

let a = [...list], r = []
while(a.length) r.push(a.splice(0,1+a.indexOf('')).slice(0,-1))

console.log(r)

edited Dec 11, 2022 at 18:59

answered Dec 11, 2022 at 18:29

Andrew Parks

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Comments

Peter Seliger · Accepted Answer · 2022-12-11 21:41:39Z

1

console.log(
  String(
    ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""]
  //["", "1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""]
  )
  .split(',,')
  .map(str => 
    str
      .replace(/^,|,$/, '')
      .split(',')
  )
);

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

answered Dec 11, 2022 at 21:41

Peter Seliger

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Comments

Ronnie Smith · Accepted Answer · 2022-12-11 22:01:37Z

1

Convert it to a string, .split it, then .map it to a function making a new array with each .split item.

var list = ["1", "2", "3", "", "4", "5", "6", "", "7", "8", "9", ""];
console.log(list.toString().split(",,").map(x => x.split(",").filter(y => y.length > 0)));

edited Dec 11, 2022 at 22:01

answered Dec 11, 2022 at 20:08

Ronnie Smith

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3 Comments

Andrew Parks Over a year ago

Each subarray contains a string, rather than 3 elements

Andrew Parks Over a year ago

Hehe now your last subarray has an empty string in it...

Ronnie Smith Over a year ago

@AndrewParks thank you! It's gone now. I'm thinking if I could add about 50 lines of code to my answer it might get an upvote here ;-)

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