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Online Sandbox for SQL and PHP: Write, Run, Test, and Share SQL Queries and PHP Code
<?php
$arr = [1, 3, 4, 6, 4, 2, 1, 1];
$res1 = array_count_values($arr);
//var_export($res1);
$res2 = array_filter($res1, fn($el)=>($el>1));
var_export(array_keys($res2));