How to remove part of a string?

Question

PHP

There is a line: 1,2,4,5,6,7,9,15,16... i.e. any numbers through ","
The numbers can be different and in a different order, you need to remove from this line, for example 4 (1,2,5,6,7,9...)
how to implement it?

Answer 1

implode(',', array_filter(explode(',', $str), function($n) {
  return $n !== '4';
}))

or
or
substr(str_replace(',4,', ',', ",$str,"), 1, -1)

Answer 2

preg_replace('/\,4$/','',str_replace(',4,', ',',$str));