在PHP中对文本文件中的列表重新排序

Question

everyone. Very first question, so take it easy on this noob. ;)

Anyway, really stumped on something. I've got a text file with this sort of listing:

1: A C D
4: A B
5: D F
7: A E
9: B C

The goal is to somehow re-sort this list and have it appear as this:

A: 1 4 7
B: 4 9
C: 1 9
D: 1 5
E: 7
F: 5

The trick is matching and displaying those matched values. For example "A" is matched with lines 1,4 and 7, and so on. I can explode the lines into individual arrays, but after that stumps me. How would I go about taking those arrays and somehow sorting them out to make it look like the final version?

Thanks for any and all info!

UPDATE:

Code I have so far:

<?php
$string="1: A C D
4: A B
5: D F
7: A E
9: B C";
$lines = explode( "
", $string );
sort($lines);
foreach($lines as $line){
echo $line."<br>";
}

// start with this
//1: A C D
//4: A B
//5: D F
//7: A E
//9: B C

// resort and display as this
//A: 1 4 7
//B: 4 9
//C: 1 9
//D: 1 5
//E: 7
//F: 5
?>

Which produces:

1: A C D
4: A B
5: D F
7: A E
9: B C

Right now I don't care that they are not in new lines. That's not important at the moment. Right now, I need to figure out how to make it sort and appear as the 2nd code block. That is the part that puzzles me.

Hope this helps clear up things.

Answer 1

Well, you sort of gave it a try and I was bored:

//read file into array of lines
$lines = file('/path/to/file.txt', FILE_IGNORE_NEW_LINES);

//loop through the lines
foreach($lines as $line) {
    //explode on space
    $cols = explode(' ', $line);
    //loop through columns and build array with letter as key adding number to that array
    for($i=1; $i < count($cols); $i++) {
        $result[$cols[$i]][] = trim($cols[0], ':');
    }
}
//sort by key (or sort $output later)
ksort($result);

//loop through and build new lines
foreach($result as $key => $vals) {
    $output[] = "{$key}: " . implode(' ', $vals);
}
//write lines to file
file_put_contents('/path/to/file.txt', implode("
", $output));