error encountered when creating arrays from a seed array using array_map

Question

I'm trying to create $scenario['B'] and $scenario['C'] using $scenario['A'] as seed data. The desired final arrays are:

$scenario['A'] = [  1,   2,   3,   4,   5,   6,   7,   8];
$scenario['B'] = [101, 102, 103, 104, 105, 106, 107, 108];
$scenario['C'] = [201, 202, 203, 204, 205, 206, 207, 208];

I have tried the following but get an error message: Notice: Undefined variable: value in test.php on line 32.

$scenario['A'] = range(1, 8);
    foreach(['B' => 100, 'C' => 200] as $key => $value):
        $scenario[$key] = array_map(function($element) {return $element + $value;}, $scenario['A']);
    endforeach;

I have tried changing part of the array_map to be function($element, $value) but that results in a different error Warning: Missing argument 2 for... Why can't it see $value? How can this be modified so it works?

This works:

$scenario['A'] = range(1, 8);
foreach(['B' => 100, 'C' => 200] as $key => $value):
    $constant_array = array_fill(0, sizeof($scenario['A']), $value);
    $scenario[$key] = array_map(function($element, $constant) {return $element + $constant;}, $scenario['A'], $constant_array);
endforeach;

Per http://php.net/manual/en/function.array-map.php "The number of parameters that the callback function accepts should match the number of arrays passed to the array_map()". The reason function($element, $value) did not work was because only 1 array was being passed to the array_map(). It is necessary to make $constant_array that is the same size as the seed array, $scenario['A'], so that all elements in the seed array are affected by array_map().

But I like the answer provided by @Nigel Ren more.

You probably need function($element) use($value) {

Nigel Ren
– Nigel Ren

2017-12-16 17:07:40 +00:00
Commented Dec 16, 2017 at 17:07 — Nigel Ren
– Nigel Ren, Commented Dec 16, 2017 at 17:07

Nigel Ren · Accepted Answer · 2017-12-16 17:09:52Z

2

You need to add the use to your function call...

$scenario['A'] = range(1, 8);
foreach(['B' => 100, 'C' => 200] as $key => $value):
    $scenario[$key] = array_map(function($element) use ($value) 
            {return $element + $value;}, $scenario['A']);
endforeach;
print_r($scenario['B']);

Gives...

Array
(
    [0] => 101
    [1] => 102
    [2] => 103
    [3] => 104
    [4] => 105
    [5] => 106
    [6] => 107
    [7] => 108
)

answered Dec 16, 2017 at 17:09

Nigel Ren

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