- json_decode: documentation ( source)
- in_array: documentation ( source)
<?php
$arrayList = "20891,20892,20896,20897,20898,20901,20902,20903,20904,20905";
$product_item = array('pid' => 20891);
if(in_array($product_item['pid'], json_decode("[".$arrayList."]"))) { print "Found it!"; }