- array_column: documentation ( source)
- array_search: documentation ( source)
<?php
$tags = [];
$tags[] = [
"name" => "Farmacia",
"lastUpdated" => "2018-02-14 21:07:42"
];
$tags[] = [
"name" => "Farmacia2",
"lastUpdated" => "2018-02-14 21:07:42"
];
$tags[] = [
"name" => "Farmacia3",
"lastUpdated" => "2018-02-14 21:07:42"
];
$res = array_search('Farmacia4', array_column($tags, 'name'));
echo $res;