php for loop to remove common words - php

Question

I have a text file that maintains a list of words.
What I am trying to do is pass a string(sentence) to this function and remove the word from the string if it exists in the text file.
<?php
error_reporting(0);
$str1= "the engine has two ways to run: batch or conversational. In batch, expert system has all the necessary data to process from the beginning";
common_words($str1);
function common_words($string) {
$file = fopen("common.txt", "r") or exit("Unable to open file!");
$common = array();
while(!feof($file)) {
array_push($common,fgets($file));
}
fclose($file);
$words = explode(" ",$string);
print_r($words);
for($i=0; $i <= count($words); $i+=1) {
for($j=0; $j <= count($common); $j+=1) {
if($words[$i] == $common[$j]){
unset($words[$i]);
}
}
}
}
?>
It doesn't seem to work however. The common words from the string are not being removed. instead I am getting the same string with the one I started.
I think I am doing the loop wrong. What is the correct approach and what am I doing wrong?

Answer 1

on the line
if($words[$i] == $common[$j]){
change it to
if(in_array($words[$i],$common)){
and remove the second for loop.

Answer 2

Try using str_replace():
foreach($common as $cword){
str_replace($cwrod, '', $string); //replace word with empty string
}
Or in full:
<?php
error_reporting(0);
$str1= "the engine has two ways to run: batch or conversational. In batch, expert system has all the necessary data to process from the beginning";
common_words($str1);
function common_words(&$string) { //changes the actual string passed with &
$file = fopen("common.txt", "r") or exit("Unable to open file!");
$common = array();
while(!feof($file)) {
array_push($common,fgets($file));
}
fclose($file);
foreach($common as $cword){
str_replace($cword, '', $string); //replace word with empty string
}
}
?>