PHP How to echo an array key if value exists in multidimensional array

Question

In the following array I would like to search for firstname, eg tom and then echo out the name of the key "library" and "canteen" because there is stored a person with first name tom in both of them.

This is the output of print_r($school);

Array
(
    [library] => Array
         (
            [0] => Array
                (
                    [firstname] => tom
                    [lastname] => brown
                )
        )
)
Array
(
    [canteen] => Array
        (
            [0] => Array
                (
                    [firstname] => matt
                    [lastname] => smith

                )
            [1] => Array
                (
                    [firstname] => tom
                    [lastname] => jones
                )
        )
)

I've done multiple tries with foreach loops without success. I must admit that I'm not completely familiar with the way they work.

This is what I've tried:

foreach ($school as $k => $v) {
    if ($v['firstname'] == 'tom'){
        echo 'Currently at the '.$k.'<br>';
    }
}

This is the output is whish for:

Currently at the library
Currently at the canteen

Answer 1

You'll need another foreach loop

foreach ($school as $k => $v) {
    foreach($v as $key => $value){
        if ($value['firstname'] == 'tom'){
            echo 'Currently at the ' . $k;
        }
    }
}

Answer 2

The problem is you are only iterating trough the first dimension, but you array is twodimensional. Here is the fixed code:

foreach ($school as $k => $va) { //Iterate trough the array $school($k is the key and $va is the value)
 foreach($va as $v) { //Iterate trough $va, this is a multidimensional array. $v is the value.
  if ($v['firstname'] == 'tom'){ 
   echo 'Currently at the '.$k; //$k is still storing the key from the first foreach.
  }
 }
}

Foreach is not hard, but you will need to understand it first. Here is "what the computer says" hen running the code: Ok, Iterate trough the array $school. Now I will store the key library in $k, and value array(...) in $va.
Oh, another foreach... Now I should loop through $va(the value of $school['library']). I should set the $v['firstname'] to 'tom' and the lastname to 'brown'.
The check is ok, echo the key 'library'.
Foreach exits, no more entry in 'library'.
The first foreach is still alive: It should set the $k to canteen and $va to array(...).
Starting new foreach, iterating trough $va($school['canteen']), put key 'canteen' to $k...
$v is now Array("firstname" => "matt", "lastname" => "smith");
Firstname is not 'tom'. Next value from school[canteen].
$v is now Array("firstname" => "tom", "lastname" => "jones");
Firstname is tom, echoing key from $k, it is 'canteen'.
End of array, both foreach exits.

Answer 3

if $school is the outer array then you can do like this:

foreach ($school as $k => $v) {
 foreach($v as $key=>$value{
if ($value['firstname'] == 'tom'){
    echo 'Currently at the '.$key;
}
}
}

Answer 4

You're using multidimensional array. Therefore, you need to use two foreach loops to loop through each array.