PHP替换多个单词

So I want to remove everything but some words. I want to keep for an example "car", "circle" and "roof". But remove everything else in a string.

Let's say the string is "I have a car with red one circle at the roof". I wantr to remove everything but "car", "circle" and "roof".

I know there's this one:

$text = preg_replace('/\bHello\b/', 'NEW', $text);

But I can't figure out how to do it with multiple words. I've done this below, but it does the opposite.

$post = $_POST['text'];
$connectors = array( 'array', 'php', 'css' );

$output = implode(' ', array_diff(explode(' ', $post), $connectors));

echo $output;

<?php
$wordsToKeep = array('car', 'circle', 'roof');
$text = 'I have a car with red one circle at the roof';

$words = explode(' ', $text);
$filteredWords = array_intersect($words, $wordsToKeep);

$filteredString = implode(' ', $filteredWords);

$filteredString would then equal car circle roof.

See http://php.net/manual/en/function.array-intersect.php

For the sake of reusability, you can create a function like this:

function selector($text,$selected){
$output=explode(' ',$text);

foreach($output as $word){
if (in_array($word,$selected)){
$out[]= trim($word);
}
}
return $out;
}

You get an array like this:

echo implode(' ',selector($post,$connectors));

I suggest the str_word_count() function:

<?php

$string = "Hello fri3nd, you're
       looking          good today!
       I have a car with red one circle at the roof.
       An we can add some more _cool_ stuff :D on the roof";

// words to keep
$wordsKeep = array('car', 'circle', 'roof');

// takes care of most cases like spaces, punctuation, etc.
$wordsAll = str_word_count($string, 2, '\'"0123456789');

// remaining words
$wordsRemaining = array_intersect($wordsAll, $wordsKeep);

// maybe do an array_unique() here if you need

// glue the words back to a string
$result = implode(' ', $wordsRemaining);

var_dump($result);