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@SeanCannon
Last active April 26, 2024 09:43
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PHP array_flatten() function. Convert a multi-dimensional array into a single-dimensional array.
<?php
/**
* Convert a multi-dimensional array into a single-dimensional array.
* @author Sean Cannon, LitmusBox.com | seanc@litmusbox.com
* @param array $array The multi-dimensional array.
* @return array
*/
function array_flatten($array) {
if (!is_array($array)) {
return false;
}
$result = array();
foreach ($array as $key => $value) {
if (is_array($value)) {
$result = array_merge($result, array_flatten($value));
} else {
$result = array_merge($result, array($key => $value));
}
}
return $result;
}
@brandonmcconnell
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@sayhicoelho Have you tried my approach above? It should work with associative and non-associative arrays, and be compatible with PHP 7+.

It also supports a depth parameter, so you can easily flatten only the top layer, the first N layers, or infinitely.

@graceman9
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@brandonmcconnell Using my sample data it gives not what I expected.
By the way, how to use it with unlimited $depth? array_flatten($r, 999) doesn't look good for me
Despite of that your function does the job of flattening, no doubt :) maybe flatten is not the right word because of ambiguity?

@sayhicoelho thanks for 7.x support!

echo json_encode(array_flatten($r, 9));
{
    "a": "value1",
    "c": "value1.1",
    "d": "value1.2",
    "e": "value2",
    "k": "value2.1",
    "m": "value2.2",
    "n": "value2.3",
    "o": "value3",
    "0": "first",
    "1": "second",
    "q": "value5"
}

@brandonmcconnell
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@graceman9 What data produces an unexpected result?

For infinite depth, just use -1

@graceman9
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@brandonmcconnell Have you noticed the difference?

{
    "a": "value1",
    "b_c": "value1.1",
}

and

{
    "a": "value1",
    "c": "value1.1",
}

@brandonmcconnell
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@graceman9 Oh you want the keys to be concatenated, so every key keeps the log of its original path. Yeah, you are correct that my version does not do that. I tried to follow the approach common in other languages. 🙂

@boedy
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boedy commented Apr 26, 2024

For a simple 2D array:

$multiDimArray = [[1, 2], [3, 4], [5, 6]];
$flatArray = array_reduce($multiDimArray, 'array_merge', []);

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