- array_column: documentation ( source)
- print_r: documentation ( source)
- array_unique: documentation ( source)
<?php
$arr = Array ( 0 => Array ( 0 => 'Red', 1 => 'Steel' ),
1 => Array ( 0 => 'Red', 1 => 'Wood' ) ,
2 => Array ( 0 => 'Blue', 1 => 'Wood' )
);
$colors = array_unique(array_column($arr, 0));
$materials = array_unique(array_column($arr, 1));
print_r($colors);print_r($materials);