need advice with logic for coding out this php exercise - php

Question

I've got a list in a text file with the top 1000 words used in the english language. Each line has a list of up to 50 words, like this:
the,stuff,is,thing,hi,bye,hello,a,stuffs
cool,free,awesome,the,pray,is,crime
etc.
I need to write code using that file as input, to make an output file with the a list of pairs of words which appear together in at least fifty different lists. For example, in the above example, THE & IS appear together twice, but every other pair appears only once.
I can't store all possible pairs of words, so no brute force.
I'm trying to learn the language and I'm stuck on this exercise of the book. Please help. Any logic, guidance or code for this would help me.
This is what I have so far. It doesn't do what's intended but I'm stuck:
Code:
//open the file
$handle = fopen("list.txt", 'r');
$count = 0;
$is = 0;
while(!feof($handle)) {
$line = fgets($handle);
$words = explode(',', $line);
echo $count . "<br /><br />";
print_r($words);
foreach ($words as $word) {
if ($word == "is") {
$is++;
}
}
echo "<br /><br />";
$count++;
}
echo "Is count: $is";
//close the file
fclose($handle);
$fp = fopen('output.txt', 'w');
fwrite($fp, "is count: " . $is);
fclose($fp);
This is what I came up with but I think it's too bloated:
plan:
check the first value of the $words array
store the value into $cur_word
store $cur_word as a key in an array ($compare) and
store the counter (line number) as the value of that key
it'll be 1 at this point
see if $cur_word is on each line and if it is then
put the value into $compare with the key as $cur_word
if array has at least 50 values then continue
else go to the next value of the $words array
if it has 50 values then
go to the next value and do the same thing
compare both lists to see how many values match
if it's at least 50 then append
the words to the output file
repeat this process with every word

Answer 1

There are probably 100's of solutions to this problem. Here is one
$contents = file_get_contents("list.txt");
//assuming all words are separated by a , and converting new lines to word separators as well
$all_words = explode(",", str_replace("\n", ",", $contents));
$unique_words = array();
foreach ($all_words as $word) {
$unique_words[$word] = $word;
}
this will give you all the unique words in the file in an array.
You can also use the same technique to count the words
$word_counts = array();
foreach ($all_words as $word) {
if (array_key_exists($word, $word_counts)) {
$word_counts[$word]++;
} else {
$word_counts[$word] = 1;
}
}
then you can loop through and save the results
$fp = fopen("output.txt", "w");
foreach ($word_counts as $word => $count) {
fwrite($fp, $word . " occured " . $count . " times" . PHP_EOL);
}
fclose($fp);