PHP array_reduce with initial parameter as an array

Question

I have this initial array:

[
    0 => ['id' => 5, 'value' => 50],
    1 => ['id' => 6, 'value' => 60],
    2 => ['id' => 7, 'value' => 70],
]

and want to convert it to:

[
    5 => ['value' => 50],
    6 => ['value' => 60],
    7 => ['value' => 70],
]

At first, I tried to use map, but it can't modify the array keys, so I thought reduce would solve the problem because it reduces the array to a single value, in this case, an array. So I tried:

array_reduce(
    $array,
    function($carry, $item) {
        return $carry[$item['id']] = $item['value'];
    },
    []
);

But it returns this error Cannot use a scalar value as an array. What am I doing wrong? Does array_reduce cannot receive an array as an initial value?

I'm trying to do it as functional as I can, I know a simple foreach would solve the problem. — Mathius17
– Mathius17, Commented May 6, 2016 at 15:16
Not really what array_reduced is supposed to do at all: $newArray = array_column($oldArray, 'value', 'id'); array_walk($newArray, function(&$value) { $value = ['value' => $value]; }); Demo — Mark Baker
– Mark Baker, Commented May 6, 2016 at 15:16
Oh, that works. If you post the answer I will gladly accept it — Mathius17
– Mathius17, Commented May 6, 2016 at 15:21

Aleksandar · Accepted Answer · 2019-02-01 08:22:03Z

6

Your array_reduce didn't work because You weren't returning the accumulator array (carry in Your case) from the callback function.

array_reduce(
    $array,
    function($carry, $item) {
        $carry[$item['id']] = $item['value'];
        return $carry; // this is the only line I added :)
    },
    []
);

I came to this question while looking for a way to use array_reduce, so I felt I should write this comment. I hope this will help future readers. :)

answered Feb 1, 2019 at 8:22

Aleksandar

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2 Comments

FroboZ Over a year ago

This should be the accepted answer I think. I was doing return $list[$client->ID] = $client->post_title; which didn't produce the correct array if I just put it on its own line and hten returned list it worked.

Aleksandar Over a year ago

@ChristopherKarlsson thank You! I am glad this helped with Your issue :) However, I will let the author decide whether this will become the accepted answer. I think he already did, but it' never too late. Regards, Aleksandar

Murad Hasan · Accepted Answer · 2016-05-06 15:29:47Z

As Mark Bakerdid it. I also did with foreach loop.

$arr = array(
            array('id' => 5, 'value' => 50),
            array('id' => 6, 'value' => 60),
            array('id' => 7, 'value' => 70)
        );

$result = array();
$result = array_column($arr, 'value', 'id'); 
array_walk($result, function(&$value) { $value = ['value' => $value]; });


//I did this using foreach loop, But the OP need it through array function.
//foreach($arr as $key => $value){
//    $result[$value['id']] = array('value' => $value['value']);
//}

echo '<pre>';
print_r($result);

Result:

Array
(
    [5] => Array
        (
            [value] => 50
        )

    [6] => Array
        (
            [value] => 60
        )

    [7] => Array
        (
            [value] => 70
        )

)

rharvey · Accepted Answer · 2016-05-06 15:27:39Z

1

Sometimes the best solutions are the simplest. Loop through your array and assign the id and value to a new array.

$new_array = array();    
foreach ($array as $key => $arr) {
    $new_array[$arr['id']] = array('value' => $arr['value']);
}

answered May 6, 2016 at 15:27

rharvey

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2 Comments

Mathius17 Over a year ago

I know, i know, is just that I wanted to do it as functional as possible. But thanks anyway!

rharvey Over a year ago

I totally get that. I think the issue would be with using array_map or array_walk is that you would have an issue converting the keys/indexes i.e. from 0 to 5. At least this way it's very little code for the results you need.

Ryan · Accepted Answer · 2017-06-08 02:18:18Z

0

You can do it functionally. I suspect it's not actually more readable however.

array_combine(
    array_column($a, 'id'), 
    array_map(function($v) { return ['value' => $v['value']]; }, $a)
);

Or even...

array_map(
  function($v) { return ['value' => $v['value']]; }, 
  array_column($a, null, 'id')
)

answered Jun 8, 2017 at 2:18

Ryan

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Comments

Evgeniy · Accepted Answer · 2018-06-05 17:51:22Z

0

array_reduce($ar, function ($acc, $item) {
        $acc[$item['id']] = [ 'value' => $item['value']]; 
        return $acc;
    }, [])

answered Jun 5, 2018 at 17:51

Evgeniy

1

1 Comment

Alexander Over a year ago

While this code may answer the question, providing additional context regarding how and why it solves the problem would improve the answer's long-term value.

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