How do I join an array with the result not being a string in Javascript?

Question

I have an array [1,2,3,4,5,6] and a separator '~' and I want to joint them into a new array with '~' being the separator.

I'd like the output to be [1,'~', 2,'~', 3,'~', 4,'~', 5,'~', 6].

Using Lodash I got something like:

var my_array = [1,2,3,4,5,6]
var separator = '~'
_.flatten(_.zip(my_array, new Array(my_array.length).fill(separator)))

But this feels ugly and I'm sure there is a better way.

EDIT: Even though the array above has ints I'd like this to work for any type of object.

A nice simple loop will do the trick, but will mandate a manual `-1` in the length. Was looking for something a little more pretty. — Agam Rafaeli-Farhadian, Feb 28 '17 at 11:48
`join` is an ugly operation to implement because it has an inherent break of the symmetry. — Aur Saraf, Feb 28 '17 at 11:50
@T.J.Crowder in order for this to be actually simple the loop will have to run for `my_array.length - 1` times. No? — Agam Rafaeli-Farhadian, Feb 28 '17 at 11:52
The question has been closed, but a single line ES6 would be: `var r = Array.from({ length: (a.length * 2) - 1 }, (v, i) => i % 2 ? s : a[i/2] );` Where `a` is your array and `s` is your "~". Codepen: http://codepen.io/cjke/pen/pejPOQ?editors=0010 — Chris, Feb 28 '17 at 14:14
I'm a bit bored - here is an even shorter one: `var r = a.reduce((c, v) => [...c, v, s], []).slice(0, -1)` Codepen: http://codepen.io/cjke/pen/WpQPKz?editors=0010 — Chris, Mar 01 '17 at 03:20
@AgamRafaeli I mean it does something to all of the array values *but one*. — Aur Saraf, Mar 09 '17 at 08:13

winner_joiner · Answer 1 · 2017-02-28T12:58:47.403

8

Why not in pue Javascript:

Minor Update: to account for values greater then 9

first join it to a string my_array.join("~")
then split every char .split(/\b/gi)

var my_array = [1,2,3,4,5,6,10,11]
var separator = '~'

console.info(my_array.join("~").split(/\b/gi));

Update (even if closed):

In Regard to point, other Objects. This should work, even if not a one-liner.

var myArray = [1,2,3,45,6,10,new Date()];

var newArray = myArray.reduce((p,n)=>{ 
  if(p.length){
    p.push("~");
  }
  p.push(n);
  return p;
},[]);

console.info(newArray)

edited Feb 28 '17 at 12:58

answered Feb 28 '17 at 11:48

winner_joiner

12,173
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4

And it blows up as soon as there's a `10` or higher in the array, or a value less than `0`, or something other than a number, or, or, or... – T.J. Crowder Feb 28 '17 at 11:50
Also, it assumes a good toString implementation for each of the objects. – Agam Rafaeli-Farhadian Feb 28 '17 at 11:53
@T.J.Crowder now it should work with 10 and higher – winner_joiner Feb 28 '17 at 11:58
3

This fails if the array is not toString-able for example dates. – Benjamin Gruenbaum Feb 28 '17 at 11:59
1

It's still a horrible way to approach this with lots of other failure modes (including those negative numbers I mentioned). – T.J. Crowder Feb 28 '17 at 12:00
@T.J.Crowder if you change comments,it is impossible to answer correctly to one. – winner_joiner Feb 28 '17 at 12:01
1

Un huh, that was 10 minutes before your update (and obvious). – T.J. Crowder Feb 28 '17 at 12:02

score 5 · Accepted Answer · answered Feb 28 '17 at 11:54

5

Nice simple forEach without a dozen temporary arrays, etc.:

var my_array = [1,2,3,4,5,6];
var result = [my_array[0]];
my_array.forEach(function(entry, index) {
  if (index > 0) {
    result.push("~", entry);
  }
});
console.log(result);

Or you can get rid of the if with a single temporary array:

var my_array = [1,2,3,4,5,6];
var result = [my_array[0]];
my_array.slice(1).forEach(function(entry, index) {
  result.push("~", entry);
});
console.log(result);

answered Feb 28 '17 at 11:54

T.J. Crowder

1,031,962
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1

FTW!! Thank you!! – Agam Rafaeli-Farhadian Feb 28 '17 at 11:58
1

@AgamRafaeli: It does assume at least one entry in the array, so if that assumption is invalid, the `var result...` line becomes `var result = my_array.length ? [my_array[0]] : [];` :-) – T.J. Crowder Feb 28 '17 at 12:15

Benjamin Gruenbaum · Answer 3 · 2017-02-28T12:10:00.920

3

Just throwing my hat in:

arr.map(x => [x, '~']).reduce((p, c) => p.concat(c));

This isn't very hacky, it maps every element into two elements and concats them together, it is pretty easy to generalize:

const intercalate = (arr, sep) => arr.map(x => [x, sep])
                                     .reduce((p, c) => p.concat(c))
                                     .slice(0, -1);

Or with a single reduce:

const intercalate = (arr, sep) => arr.reduce((p, c) => p.concat(c, sep)).slice(0, -1);

edited Feb 28 '17 at 12:10

answered Feb 28 '17 at 12:05

Benjamin Gruenbaum

270,886
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for `arr = [1,2,3]` this returns `[1, "~", 2, "~", 3, "~"]`. Maybe add slice(0,-1) at the end? – Agam Rafaeli-Farhadian Feb 28 '17 at 12:08

Lix · Answer 4 · 2017-02-28T11:58:46.750

2

Here is an option using forEach -

var a = [1,2,3]
var sep = '~'
var b = []
a.forEach(function(x) { b.push(x, sep) })
b.pop() // remove the last `~`

edited Feb 28 '17 at 11:58

answered Feb 28 '17 at 11:51

Lix

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zahirdhada · Answer 5 · 2017-02-28T12:18:10.547

1

Using _.flatMap,

var my_array = [1,2,3,4,5,6];
var separator = '~';
console.log(_.flatMap(my_array, function( v ){ return [v,separator] }).slice(0,-1));

Update:

Ensure trailing ~ is removed.

edited Feb 28 '17 at 12:18

answered Feb 28 '17 at 12:00

zahirdhada

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This will leave trailing `~` – RaR Feb 28 '17 at 12:01

Nina Scholz · Answer 6 · 2017-02-28T12:01:56.563

0

You could use Array#reduce and concat a tilde if necessary.

var array = [1, 2, 3, 4, 5, 6],
    result = array.reduce(function (r, a, i) {
        return r.concat(i ? '~' : [], a);
    }, []);
    
console.log(result);

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

Anosther proposal with Array#forEach

var array = [1, 2, 3, 4, 5, 6],
    result = [];

array.forEach(function (a) {
   result.push(a, '~');
});

result.length--;
    
console.log(result);

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

edited Feb 28 '17 at 12:01

answered Feb 28 '17 at 11:51

Nina Scholz

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All those unnecessary temporary arrays!! – T.J. Crowder Feb 28 '17 at 11:53

Idan · Answer 7 · 2017-02-28T12:00:13.357

0

Using a traditional for loop

var nums = [1,2,3,4,5,6];
var dash = '~';

var res = [];
for (var i=0; i<nums.length; i++){
  res.push(nums[i]);
  res.push(dash);
}
res.pop();

console.log(res);

edited Feb 28 '17 at 12:00

answered Feb 28 '17 at 11:56

Idan

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This as of now results in [1, "~", 2, "~", 3, "~", 4, "~", 5, "~", 6, "~"] where the desired result [1, "~", 2, "~", 3, "~", 4, "~", 5, "~", 6] – Agam Rafaeli-Farhadian Feb 28 '17 at 11:58
1

Sorry, corrected. – Idan Feb 28 '17 at 12:00

How do I join an array with the result not being a string in Javascript?

7 Answers7