Obtain key from array through value - php

Question

How can I obtain a key in a array just by knowing it's value? For example, here is an array:
$array = Array("Item1" => array("Number" => "One", "Letter" => "A"));
Just by knowing "One" or "A", how can I get the main key name, Item1?
I've looked into array_key_value and in_array but I do not think that those functions are helpful for my kind of array.

Answer 1

Since it is a 2d array, you will want to search the inner array for the value so you would have to make your own function to do this. Something like this:
function findInArray($array, $lookup){
//loop over the outer array getting each key and value.
foreach($array as $key=>$value){
//if we found our lookup value in the inner array
if(in_array($lookup, $value)){
//return the original key
return $key;
}
}
//else, return null because not found
return null;
}
$array = Array("Item1" => array("Number" => "One", "Letter" => "A"));
var_dump(findInArray($array, 'One')); //outputs string(5) "Item1"
var_dump(findInArray($array, 'Two')); //outputs null
Demo: https://3v4l.org/oRjHK

Answer 2

This function may help you
function key_of_value($array, $value){
foreach($array as $key=>$val){
if(in_array($value, $val)){
return $key;
}
}
return null;
}
echo key_of_value(['Item1'=>['One','Two','Three','Hello',2,6]],'A');

Answer 3

There is no way around iterating through your data. This might be a little more elegant than two foreach loops:
<?php
$match = null;
$needle = 'Two';
$haystack = [
'Item1' => [
'Number' => 'One',
'Letter' => 'A'
],
'Item2' => [
'Number' => 'Two',
'Letter' => 'B'
],
'Item3' => [
'Number' => 'Three',
'Letter' => 'C'
],
];
array_walk($haystack, function($entry, $key) use ($needle, &$match) {
if(in_array($needle, $entry)) {
$match = $key;
}
});
var_dump($match);
The output obviously is:
string(5) "Item2"

Answer 4

You can use array_walk_recursive to iterate on array values recursive. I write a function that return main key of searched value in nested arrays.
<?php
$array = array("Item1" => array("Number" => "One", "Letter" => "A", 'other' => array('Number' => "Two")));
echo find_main_key($array, 'One'); //Output: "Item1"
echo find_main_key($array, 'A'); //Output: "Item1"
echo find_main_key($array, 'Two'); //Output: "Item1"
var_dump(find_main_key($array, 'nothing')); // NULL
function find_main_key($array, $value) {
$finded_key = NULL;
foreach($array as $this_main_key => $array_item) {
if(!$finded_key) {
array_walk_recursive($array_item, function($inner_item, $inner_key) use ($value, $this_main_key, &$finded_key){
if($inner_item === $value) {
$finded_key = $this_main_key;
return;
}
});
}
}
return $finded_key;
}

Answer 5

This is how I would do it:
foreach($array as $key => $value) {
if(in_array('One', $value)) echo $key;
}