How can I implode an array while skipping empty array items?

Question

Perl's join() ignores (skips) empty array values; PHP's implode() does not appear to.

Suppose I have an array:

$array = array('one', '', '', 'four', '', 'six');
implode('-', $array);

yields:

one---four--six

instead of (IMHO the preferable):

one-four-six

Any other built-ins with the behaviour I'm looking for? Or is it going to be a custom jobbie?

You're wrong about Perl's behaviour. `join` doesn't skip undefined elements. In fact, they result in a warning. `$a[0]="a"; $a[2]="c"; say join "-",@a;` displays `Use of uninitialized value within @a in join or string` and `a--c`. One can use `join '-', grep !defined, ...` to skip undefined values. `grep !length,` will do empty strings. — ikegami, May 12 '11 at 23:01

Felix Kling · Accepted Answer · 2011-05-12T22:59:53.333

247

You can use array_filter():

If no callback is supplied, all entries of input equal to FALSE (see converting to boolean) will be removed.

implode('-', array_filter($array));

Obviously this will not work if you have 0 (or any other value that evaluates to false) in your array and you want to keep it. But then you can provide your own callback function.

edited May 12 '11 at 22:59

answered May 12 '11 at 22:52

Felix Kling

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6

Would that mean that `false`, and `0` are also thrown out? – Jess May 12 '11 at 22:54
1

@maz: Yes, but you can always provide your own callback. `empty`, as you use it, will also treat `0` and `false` as `false` (and remove it) btw. – Felix Kling May 12 '11 at 22:55
6

+1, but it has to be mentioned, that `array_filter()` by default filters off every `false`, `null`, empty string ('') and `0`. – Tadeck May 12 '11 at 22:55
1

@Tadeck: Yes, just follow the link in the quote. Even more values are considered as `false`: empty array, `0.0` and `"0"`. – Felix Kling May 12 '11 at 22:58
@Felix: I knew it - just wanted to stress it for people new in PHP ;) Anyway: thank you – Tadeck May 12 '11 at 23:05
Nice trick - didn't know array_filter can work without callback :) – Andis Mar 21 '22 at 15:52

Jess · Answer 2 · 2011-05-12T23:14:57.380

9

I suppose you can't consider it built in (because the function is running with a user defined function), but you could always use array_filter.
Something like:

function rempty ($var)
{
    return !($var == "" || $var == null);
}
$string = implode('-',array_filter($array, 'rempty'));

edited May 12 '11 at 23:14

answered May 12 '11 at 22:53

Jess

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Using `empty` has the same effect as passing no callback at all. *Edit: You have to negate the return value. Otherwise only empty elements will be returned ;) (actually using `empty` as you did before was also wrong)* – Felix Kling May 12 '11 at 23:03
1

Yeah, that's backward. But you gave me the right idea `implode('-', array_filter($ary, create_function('$a', 'return $a!="";')));` – Tom Auger May 12 '11 at 23:12

score 8 · Answer 3 · edited Apr 05 '18 at 15:43

8

To remove null, false, empty string but preserve 0, etc. use func. 'strlen'

$arr = [null, false, "", 0, "0", "1", "2", "false"];
print_r(array_filter($arr, 'strlen'));

will output:

//Array ( [3] => 0 [4] => 0 [5] => 1 [6] => 2 [7] => false )

edited Apr 05 '18 at 15:43

ElasticCode

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answered Apr 05 '18 at 14:48

Ali Varli

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score 3 · Answer 4 · answered May 12 '11 at 23:10

How you should implement you filter only depends on what you see as "empty".

function my_filter($item)
{
    return !empty($item); // Will discard 0, 0.0, '0', '', NULL, array() of FALSE
    // Or...
    return !is_null($item); // Will only discard NULL
    // or...
    return $item != "" && $item !== NULL; // Discards empty strings and NULL
    // or... whatever test you feel like doing
}

function my_join($array)
{
    return implode('-',array_filter($array,"my_filter"));
}

score 2 · Answer 5 · answered Jun 29 '20 at 00:38

2

$array = ["one", NULL, "two", NULL, "three"];
$string = implode("-", array_diff($array, [NULL]));
echo $string;

Returns one-two-three

answered Jun 29 '20 at 00:38

Ryan Prescott

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1

score 1 · Answer 6 · answered May 12 '11 at 22:56

Based on what I can find, I'd say chances are, there isn't really any way to use a PHP built in for that. But you could probably do something along the lines of this:

function implode_skip_empty($glue,$arr) {
      $ret = "";
      $len = sizeof($arr);
      for($i=0;$i<$len;$i++) {
          $val = $arr[$i];    
          if($val == "") {
              continue;
          } else {
            $ret .= $arr.($i+1==$len)?"":$glue;
          }
      }
      return $ret;
}

score 1 · Answer 7 · answered May 12 '11 at 22:56

1

Try this:

$result = array();

foreach($array as $row) { 
   if ($row != '') {
   array_push($result, $row); 
   }
}

implode('-', $result);

answered May 12 '11 at 22:56

Jeremy

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score -1 · Answer 8 · answered Nov 04 '17 at 13:05

array_fileter() seems to be the accepted way here, and is probably still the most robust answer tbh.

However, the following will also work if you can guarantee that the "glue" character doesn't already exist in the strings of each array element (which would be a given under most practical circumstances -- otherwise you wouldn't be able to distinguish the glue from the actual data in the array):

$array = array('one', '', '', 'four', '', 'six');
$str   = implode('-', $array);
$str   = preg_replace ('/(-)+/', '\1', $str);

score -3 · Answer 9 · answered Dec 02 '13 at 08:00

-3

Try this:

if(isset($array))  $array = implode(",", (array)$array);

answered Dec 02 '13 at 08:00

user2775080

73
3

You might want to use isset() to prevent warnings. – user2775080 Dec 02 '13 at 08:01
I'm not sure how `isset()` or casting the input array as `array` addresses any of the concerns of the original post? – Tom Auger Dec 07 '13 at 03:29
2

This is not a solution. Casting to (array) does not remove empty items from the array. – mjwunderlich Jul 15 '15 at 15:29

How can I implode an array while skipping empty array items?

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