Transpose query result set [duplicate] - php

Question

This question already has answers here:
Transposing multidimensional arrays in PHP
(12 answers)
Chunk and transpose a flat array into rows with a specific number of columns
(3 answers)
Closed 5 months ago.
So I have a database with players names and their skill level.
It looks like this:
Id | Name | Level
1 | Peter | 24
2 | Andy | 23
...
24 | John | 1
The first player in the list with the highest level is the strongest one, and the last is the weakest.
I need to sort them in groups with 4 players, so if I have 24 people there will be 6 groups.
The way I need to sort it I call "zig-zag".
It goes like this:
Ag Bg Cg Dg Eg Fg
01 02 03 04 05 06
12 11 10 09 08 07
13 14 15 16 17 18
24 23 22 21 20 19
So the A group will consist of players: 1, 12, 13, 24.
B group of players: 2, 11, 14, 23.
C group of players: 3, 10, 15, 22 and so on.
It's easy to do it by hand, but how I could automate this sort with PHP language?
The groups should be array list (I think so) which could I easily put to the group tables in database.

Answer 1

The idea would be to:
Sort your starting data (or preferably, start with it sorted).
Split it into chunks, basically one per each of your rows.
Reverse the order of every other chunk.
Flip the matrix so you've got your groups - one per column instead of one per row.
Example:
// Basic sample data.
$players = range(1, 24);
// Sort them ascending if you need to.
sort($players);
// Make a matrix. 2d array with a column per group.
$matrix = array_chunk($players, ceil(count($players)/4));
// Reverse every other row.
for ($i = 0; $i < count($matrix); $i++) {
if ($i % 2) {
$matrix[$i] = array_reverse($matrix[$i]);
}
}
// Flip the matrix.
$groups = array_map(null, ...$matrix); // PHP 5.6 with the fancy splat operator.
//$groups = call_user_func_array('array_map', array_merge([null], $matrix)); // PHP < 5.6 - less fancy.
// The result is...
print_r($groups);
Output:
Array
(
[0] => Array
(
[0] => 1
[1] => 12
[2] => 13
[3] => 24
)
[1] => Array
(
[0] => 2
[1] => 11
[2] => 14
[3] => 23
)
[2] => Array
(
[0] => 3
[1] => 10
[2] => 15
[3] => 22
)
[3] => Array
(
[0] => 4
[1] => 9
[2] => 16
[3] => 21
)
[4] => Array
(
[0] => 5
[1] => 8
[2] => 17
[3] => 20
)
[5] => Array
(
[0] => 6
[1] => 7
[2] => 18
[3] => 19
)
)