return last non-null element of each sub-array of an array

Question

Having a bi-dimensional array like this

anArray = [[1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null]];

my goal is to get as result a new array containing last element of each of the sub-arrays but also to be non-null. In this case: [3, 4, 5]

For getting the last element of each I used:

anArray.map(a => a.slice(-1)[0]); - it gets the last element of each sub-array.

For getting the last non-null element of an array it works using this:

_.findLast([1, null, 2, null], (el) => el !==null);

It works for a simple array but I don't know how to use it for a bi-dimensional array. Any ideas?

Hello Samurai Jack. Why not simple combine the answer from this question with one of the answer from these questions or the comment from this deleted question? — Andreas
– Andreas, Commented Mar 9, 2018 at 11:20
you may continue to use your underscorejs func: anArray.map((a) => a[_.findLastIndex(a, (el) => el !== null)]) — gaetanoM
– gaetanoM, Commented Mar 9, 2018 at 11:35

gurvinder372 · Accepted Answer · 2018-03-09 11:17:54Z

1

Use map and reduceRight (based on this)

var anArray = [[1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null]];
anArray.map( arr => arr.reduceRight( (a,c) => ( c != null && a == null ? c : a) , null))

answered Mar 9, 2018 at 11:17

gurvinder372

68.6k11 gold badges78 silver badges98 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Zenoo · Accepted Answer · 2018-03-09 11:21:03Z

1

You can use a combination of Array#map, Array#filter and Array#slice:

.map() will go through your initial array

.filter() will filter out the null values from your sub-arrays

.slice() will select the last element from each filtered sub-array

var anArray = [[1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null]];

var res = anArray.map(o => o.filter(n => n != null).slice(-1)[0]);

console.log(res);

edited Mar 9, 2018 at 11:21

answered Mar 9, 2018 at 11:17

Zenoo

12.9k4 gold badges48 silver badges71 bronze badges

2 Comments

Keith Over a year ago

You might be best using slice not splice or you will mutate the original array..

Zenoo Over a year ago

@Keith Corrected it :)

Nenad Vracar · Accepted Answer · 2018-03-09 11:21:13Z

1

You could use concat with spread syntax and then map and filter methods to remove null.

const anArray = [[1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null]];

const result = [].concat(...anArray.map(e => e.filter(Boolean).slice(-1)))
console.log(result)

answered Mar 9, 2018 at 11:21

Nenad Vracar

122k16 gold badges160 silver badges184 bronze badges

Comments

Nina Scholz · Accepted Answer · 2018-03-09 12:37:24Z

0

You could pop the last element for mapping.

var array = [[1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null]];
    result = array.map(o => o.filter(n => n != null).pop());

console.log(result);

answered Mar 9, 2018 at 12:37

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Comments

31piy · Accepted Answer · 2018-03-09 11:17:18Z

0

You can use Array#map in addition to _.findLast:

anArray.map(a => _.findLast(a, el => el !== null));

Working example:

let anArray = [
  [1, 2, 3],
  [null, 4, null, null],
  [1, 0, null, 5, null]
];

let result = anArray.map(a => _.findLast(a, el => el !== null));
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.5/lodash.min.js"></script>

answered Mar 9, 2018 at 11:17

31piy

23.9k6 gold badges51 silver badges69 bronze badges

Comments

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

You can try like this:

Idea:

Use map to return value for every sub-array.
Use while to loop backwards and get first not-null value.

Note: while because, most of the looping mechanism would loop over all values. To break at first match, and to reduce number of iterations, I prefer this.

var anArray = [ [1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null] ];
var result = anArray.map((subArray) => {
  var i = subArray.length - 1;
  while (i > 0) {
    if (subArray[i] !== null) {
      return subArray[i];
    }
    i--;
  }
})
console.log(result)

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Mar 9, 2018 at 11:27

Rajesh Dixit

25k5 gold badges52 silver badges86 bronze badges

Comments

pawas · Accepted Answer · 2018-03-09 11:32:32Z

0

var anArray = [[1, 2, 3], [null, 4, null, null], [1, 0, null, 5, null]];
var anArray = anArray.map(function(arr){
    return findLastTruthyElement(arr);
});
console.log(anArray);
function findLastTruthyElement(arr){
    if(!Array.isArray(arr)){
        throw 'passed element is not array';
        return undefined;
    }
    arr = arr.filter(function(item){
        if(item) return true;
        else return false;
    });
    return arr[arr.length-1];
}

answered Mar 9, 2018 at 11:32

pawas

11 silver badge2 bronze badges

Collectives™ on Stack Overflow

return last non-null element of each sub-array of an array

7 Answers 7

Comments

2 Comments

Comments

Comments

Comments

Idea:

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

2 Comments

Comments

Comments

Comments

Idea:

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related