PHP - Divide a multidimensional array depending on a field's value - php

Question

I have an initial array:
$arr0 = array(
0 => array(
'a' => 1,
'b' => 1
)
1 => array(
'a' => 2,
'b' => 1
)
2 => array(
'a' => 3,
'b' => 2
)
3 => array(
'a' => 4,
'b' => 3
)
4 => array(
'a' => 5,
'b' => 3
)
);
I wish to divide it into separate arrays depending on its members' value of the field 'b', like so:
// $arr1 contains $arr0[0] and $arr0[1] because their value of 'b' is 1.
$arr1 = array(
0 => array(
'a' => 1,
'b' => 1
)
1 => array(
'a' => 2,
'b' => 1
)
);
// $arr2 contains $arr0[2] because its value of 'b' is 2.
$arr2 = array(
0 => array(
'a' => 3,
'b' => 2
)
);
// $arr3 contains $arr0[3] and $arr0[4] because their value of 'b' is 3.
$arr3 = array(
0 => array(
'a' => 4,
'b' => 3
)
1 => array(
'a' => 5,
'b' => 3
)
);
Now, the field 'b' can have any natural number for value, so it is not always three resulting arrays that I will need.
I have found a related question (and answers) here, but my problem is specific because I don't know in advance what original values 'b' has, and how many of different values there are.
Any ideas?
(edit: $arr3 was written as $arr1)

Answer 1

foreach ($arr0 as $value) {
${"arr" . $value['b']}[] = $value;
}
// $arr1, $arr2 and $arr3 are defined
There is magic in the second line, which dynamically builds a variable name. However, that way of programming is really unwieldy; you would do better to make the results into yet another array, like this:
foreach ($arr0 as $value) {
$allarr[$value['b']][] = $value;
}
// $allarr is defined

Answer 2

foreach ($arr0 as $val) {
$b = $val ['b'];
if (!$arr$b) $arr$b = array();
$arr$b[] = $val;
}