2d multidimensional array to 1d array in php

Question

Just wondering if anyone has transformed a 2 dim array to a one dim array in php. I've yet to come across a clear explanation in php. Any suggestion would be appreciated.

What is the point of doing this? Do you just want to flatten the array for no apparent reason or do you just no want sub arrays? Or do you have a need for this? — Patrick, Aug 02 '11 at 15:05
I was looking for generic interpretations so other people with similar problems but different context can use. In each slot of this 2d array however, I have 2d points in osm format. The 1d array is for the input of a function i have written — John, Aug 02 '11 at 15:16
There are generic ways to loop through the values of a 2D array and append them sequentially to a new array. However, in cases such as yours, I assume the order of the elements is important. Have you considered writing a wrapper for your existing function that accepts the 2D array and converts it to the specific format required by the existing function? — George Cummins, Aug 02 '11 at 15:21
Yes that would be a good solution George. Thanks . However, I would need to change many functions that are interdependent and unfortunately time is of the essence. — John, Aug 02 '11 at 15:29

score 16 · Answer 1 · answered Mar 09 '17 at 10:26

16

This might be helpful to you if you fetching values from Query here you can use array function which will support in PHP 5.5+

$myfield_arr = array_column($query_result, 'myfield_name');

Say Good bye to loop! Enjoy Smart Code.

answered Mar 09 '17 at 10:26

Nikunj Dhimar

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Doug · Accepted Answer · 2013-05-10T20:12:09.320

9

Try this:

function array_2d_to_1d ($input_array) {
    $output_array = array();

    for ($i = 0; $i < count($input_array); $i++) {
      for ($j = 0; $j < count($input_array[$i]); $j++) {
        $output_array[] = $input_array[$i][$j];
      }
    }

    return $output_array;
}

edited May 10 '13 at 20:12

answered Aug 02 '11 at 15:03

Doug

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$output_array[] = $input_array[$i][$j]; $output_array has no index value – John Aug 02 '11 at 15:23
3

Assigning a value to an array without supplying an index means that the value will be appended at the end of the array. – Doug Aug 02 '11 at 16:37
Sorry @Doug i did not know that so thanks. I had already written this exactly the same but I thought it would not fill the array but just keep filling to certain number and overwrite slots on each iteration of the for loop. Thanks again for that. – John Aug 03 '11 at 09:11
@Doug, don't you need to add `$i++` and `$j++` at the end of `for` statements? – SAVAFA May 10 '13 at 19:23

score 1 · Answer 3 · edited May 23 '17 at 12:31

Try this one:

function array_to1d($a) {
    $out = array();
    foreach ($a as $b) {
        foreach ($b as $c) {
            if (isset($c)) {
                $out[] = $c;
            }
        }
    }
    return $out;
}

Notice that it includes a test to see if the value is set (non-null). An array that's a transposition of an array with rows of varying length will have null values in some cells, and this check can be helpful if you're trying to linearize such a beast.

score 1 · Answer 4 · answered Dec 17 '20 at 22:37

Your first thought should be array_reduce() whenever you have lots of something in an array and you just want one something by itself which represents them all in some way.

From the PHP docs:

array_reduce — Iteratively reduce the array to a single value using a callback function

In the case of 2D => 1D array conversion, the something is array; we have lots of them in an array but we just want one of them by itself.

function array2dTo1d($array2d)
{
    return array_reduce($array2d, function($carry, $array) {
        return array_merge($carry, $array);
    }, []);
}

var_dump(array2dTo1d(
    [
        [23423, 5454, 567],
        [4565, 687],
    ]
));

Result:

array(5) {
  [0] =>
  int(23423)
  [1] =>
  int(5454)
  [2] =>
  int(567)
  [3] =>
  int(4565)
  [4] =>
  int(687)
}

score 1 · Answer 5 · answered Aug 02 '11 at 15:15

It depends on what you need but if you want to reduce your 2d array to a 1d curve that completley fills the 2d plane you probably looking for a spatial index or a space-filling-curve. There are some famous and not so known like the z-curve, the hilbert curve, the peano curve or the moore curve. You can write such a curve with a L-system.

score 0 · Answer 6 · edited Dec 26 '19 at 15:32

The solution for rectangular 2D array is simple indeed, but I had a problem. My 2D-array consisted of 1D arrays of different lengths :

$myArray = [
    [1, 2, 3, 4],
    [5, 6, 7],
    [8, 9]
];

I came up with more generalized solution to turn any 2D array into 1D:

function array2DTo1D($arr2D) {
    $i = 0; $j = 0;
    $arr1D = [];
    while (isset($arr2D[$i][0])) {
        while (isset($arr2D[$i][$j])) {
            $arr1D[] = $arr2D[$i][$j];
            $j++;
        }
        $i++; $j = 0;
    }
    return $arr1D;
}

呂學洲 · Answer 7 · 2020-07-27T03:50:32.667

0

After PHP 5.3 there have a new function called arrray_walk_recursive

$data = [1,2,[3,4],5,[6,7,8],9];
$output = [];
array_walk_recursive($data, function($val) use (&$output) {
    $output[] = $val;
});

Notice that the $output is passed by reference

The $output will result in [1,2,3,4,5,6,7,8,9]

edited Jul 27 '20 at 03:50

answered Jul 25 '20 at 03:48

呂學洲

1,123
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2d multidimensional array to 1d array in php

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