php insert value into array of arrays using foreach

Question

I have a pretty basic question but I am stuck. I am pretty new to php and I have an array like this:

$array = array(
    'one' => 1,
    'two' => array('key1' => 'val1','key2' => 'val2'),
    'three' => array('key1' => 'val1','key2' => 'val2'),
    'four' => array('key1' => 'val1','key2' => 'val2')
);

and for each of the arrays in the array (that is, 'two, 'three', and 'four'), I want to insert 'key3' => 'val3' into those arrays.

I tried this:

foreach($array as $item) {
    if (gettype($item) == "array") {
        $item['key3'] = 'val3';
    }
}

But it doesn't work, and I'm not sure why. Using various print_r's all over the place, it seems to insert 'key3' => 'val3' into $item if I print it out in the loop, but the original array seems unchanged. I also tried a regular for loop but that didn't work either.

Solution

foreach works with a copy of $item, so you cannot modify your original array inside the foreach. One way to work around this is to use the & operator.

foreach($array as &$item) {
    if (is_array($item)) {
        $item['key3'] = 'val3';
    }
}

Another, more elegant way would be to use array_walk():

array_walk($array, function (&$v, $k) { 
    if (is_array($v)) {
        $v['key3'] = 'val3';
    }
});

This example will work from PHP 5.3, where Closures were introduced.

Comments

[moskito-x]

$item is only generated for the loop . You mean &$array['key3'] = 'val3'; !

[kapa]

@moskito-x I certainly mean what I wrote. That's the point of it. Check the foreach manual page I linked.

[moskito-x]

To change $item is useless. Will be always overwritten by the next loop.

[moskito-x]

But As foreach relies on the internal array pointer changing it within the loop may lead to unexpected behavior. therefore you have to unset the reference . unset($item); // break the reference with the last element. structures.foreach

[Benjamin Thvedt]

Thanks for the great answer. The first solution worked fine but the second solution didn't seem to work, it's obvious I need to get a little better at php. Can I just stick that & symbol anywhere? Wow that would change things. Also, thanks for the tip on using unset($item), not knowing that would have eventually sunk me somewhere down the line for sure!

[kapa]

@BenjaminThvedt Fixed the second one. Don't overuse the & operator, most of the time there is a better solution.

[Mark Carpenter Jr]

While not the answer to the question, this helped me better understand the relationship between the $key word and the $item.