PHP copy x number of array elements in a for loop

Question

There are probably lots of array questions. But I couldn't find one that answered this specific problem:

I have an associative array as a result from a database query. I loop trough it with a foreach loop. One of the columns contains a number. If that number is larger than 1, I have to duplicate that row x number of times so that the array will have x similiar rows.

I wonder how to do this?

foreach( $db_rows as $key => $value )
{  
  if( $value["number"] > 1 )
  //DUPLICATE $value and insert x number of times into $db_rows directly after $key.  
}

I assume $db_rows is a numerical array since you say you want it inserted directly after $key? — Shardj, Jun 07 '19 at 10:11
`into $db_rows directly after $key.` this to mean you want to insert rows directly after the $key row in the DB? — treyBake, Jun 07 '19 at 10:16
@treyBake - yes. If x is 6, I to have 6 identical rows at the same “place” in the array in stead of 1 row — johnohod, Jun 07 '19 at 10:20
may be of some use: https://stackoverflow.com/questions/740358/reorder-reset-auto-increment-primary-key — treyBake, Jun 07 '19 at 10:30
I don't think there's really a way to do this in a safe, automated way.. :/ — treyBake, Jun 07 '19 at 10:30
@johnohod wait.. looking at the answers, in one place you say insert after $db_rows, but in the comments you said yes to insert rows into the DB - which is it? — treyBake, Jun 07 '19 at 10:34
This question is both Unclear and Too Broad. We do not have a [mcve] and it is asking for multiple techniques (multiple questions already answered on Stack Overflow). We already have [How to repeat an array in PHP?](https://stackoverflow.com/q/2963777/2943403) — mickmackusa, Sep 28 '22 at 08:08

Kévin Bibollet · Accepted Answer · 2019-06-07T11:54:18.133

4

You could declare an empty array before the foreach loop, then populate it thanks to the original, its items' number property and a for loop:

$clone_db_rows = [];

foreach( $db_rows as $key => $value )
{  
    for ($i = 0; $i < $value['number']; $i++) {
        $clone_db_rows[] = $value;
    }
}

Test it here.

@Andreas suggests using array_fill to avoid the nested for statement.

He's right, and you could do this the following way, with array_merge:

$clone_db_rows = [];

foreach( $db_rows as $key => $value )
{  
    $clone_db_rows = array_merge(
        $clone_db_rows,            // Merge the current array with... 
        array_fill(                // ...a newly created one containing...
            0,
            $value['number'],      // ... X items equals to...
            $value                 // ... $value.
        )
    );
}

Test it here.

edited Jun 07 '19 at 11:54

answered Jun 07 '19 at 10:19

Kévin Bibollet

3,573
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I mean.. great, but how does this insert into the db after $key whilst maintaining/fixing the incrementation? – treyBake Jun 07 '19 at 10:31
1

Array_fill could remove a loop – Andreas Jun 07 '19 at 10:33
@treyBake - The question is about altering an array, not about inserting into the datatabase (or I misread the author's post). – Kévin Bibollet Jun 07 '19 at 10:33
@KévinBibollet check comment chain (unless OP misunderstood me xD) – treyBake Jun 07 '19 at 10:34
@treyBake - I think you misunderstood each other comment (you talked about BD, he talked about array only), but let's wait the autor's answer. ;) – Kévin Bibollet Jun 07 '19 at 10:35
@KévinBibollet yeah :) will rm dv in meantime (can't - recent edit has to be done haha) – treyBake Jun 07 '19 at 10:36
Added @Andreas suggestion to my post. – Kévin Bibollet Jun 07 '19 at 11:54

score 0 · Answer 2 · answered Jun 07 '19 at 10:15

0

Probably something like this :

foreach ($db_rows as $key => $value) {
    if ($value['number'] > 1) {
        for ($i = 0; $i < $value['number'] - 1; $i++) {
            $db_rows[] = $value;
        } 
    } 
}

answered Jun 07 '19 at 10:15

Geoffray Warnants

82
4

2

This doesn't answer the question, he said he wants the values inserted directly after $key – Shardj Jun 07 '19 at 10:16
This also __increases__ number of elements in array and finding another `$value['number']` in later elements will add them again, and again and again. So this foreach __never stops__. – u_mulder Jun 07 '19 at 10:18
I also thought of an infinite loop, but it's not the case: because internally, _foreach_ iterates on a copy of the array – Geoffray Warnants Jun 07 '19 at 10:32
Geoffray is correct. This is not a never ending loop. Foreach uses a copy as he says, a for loop and count() would be a never ending loop. @u_mulder – Andreas Jun 07 '19 at 12:11

score 0 · Answer 3 · edited Jun 07 '19 at 14:49

0

Direct Approach:

$array = [
    ["a" => "a", "b" => "aa", "number" => 3, "d" => 1],
    ["a" => "b", "b" => "bb", "number" => 1, "d" => 1],
    ["a" => "c", "b" => "cc", "number" => 3, "d" => 1],
];

foreach($array as $key => $value)
{
    if($value['number'] > 1) {
        array_unshift($array , $value, $value);
    }
}

echo "<pre>";
print_r($array);

take an array
check sub-array["value"] in conditions for true
append data at the beginning of the array( use array_push instead of array_unshift to insert at the end of the array)
this prevents pointer to the array unaffected until the loop ends
op did not mention any specific restrictions.

note:

check onto optimization.

EDIT - N+1 times Repeat: + Speed:

$output = [];
$times = 2; # set how many times you want to repeat it,

array_map(function($subArray) use(&$output, $times) {
    if($subArray['number']>1) {
        $output = array_merge($output, array_fill(0, $times, $subArray));
    } else {
        array_push($output, $subArray);
    }
}, $array);

PS: second approach maintains order for repeating values same value can benefit in better examination on it.

edited Jun 07 '19 at 14:49

kalehmann

4,821
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answered Jun 07 '19 at 10:35

Rohan Tandel

23
6

"this prevents pointer to the array unaffected until the loop ends" - pointer is not disturbed unless you want to – Rohan Tandel Jun 07 '19 at 10:36
I guess this also solves my problem. But the order of the elements is a bit strange. I get 2 "a" => "c" in the start of the array, and 1 at the end. – johnohod Jun 07 '19 at 10:50
@johnohod let me check ps: you can have second one working well and Fine I have tested and is good in terms on speed. – Rohan Tandel Jun 07 '19 at 11:02
@johnohod I did check that, as well I have mentioned in points, either you can use array_unshift or array_push. – Rohan Tandel Jun 07 '19 at 11:11

PHP copy x number of array elements in a for loop

3 Answers3

Direct Approach: