How to sort a table containing csv file data - php

Question

I have to sort the file data in a table depending on how the user chooses it to be sorted (only options are ascending and descending)
Here is my code for it:
if($submit=="Display"){
if ($headings=="0"){echo "<h2>Error</h2>";}
elseif ($search==""){echo "<h2>Error</h2>";}
else {
if($headings==$headings_array[0])
echo "<table border='1'>";
$f = fopen("data.csv", "r");
while ($line = fgetcsv($f)){
echo "<tr>";
foreach ($line as $cell) {
echo "<td><center>".$cell."</center></td>";
}
echo "<tr>";
}
fclose($f);
function my_sort($a, $b){
if ($a == $b) return 0;
return ($a > $b) ? -1 : 1;
}
$arr = $cell;
usort($arr, "my_sort");
print_r ($arr);
echo "</table>";
}
}
But it's not sorting. Can someone spot what's wrong with it? And if you have a more efficient way of doing this, please let me know as I have 15 headings and it would be a pain to do if statements for each of those headings.
To be clear, here is what I have to do:
For each sort field (which are the headings) that the user chooses, I have to arrange the display according to that heading
i.e if($headings==$headings_array[0])
$headings_array[0] is equal to Names therefore, the table should display the values in alphabetical (or reverse alphabetical) order of Names
Extra info:
$headings is the name of the select box
$headings_array is the array values for the select box
$search is the radio buttons containing whether the table should be sorted as ascending or descending
PHP only
Any help is appreciated!

Answer 1

I think your sort function is wrong. It's doing the same thing as sort() or rsort() would do.
usort simply compares two array elements and determines if they need to be swapped based on the value you return. Your sending in $a and $b, which should be csv lines. Then you compare the indexes that you need to and swap the lines accordingly.
You need to have it sort by the array index given by heading. maybe try something like this:
global $headings;
...
$arrayToBeSorted = array();
// send in an array of lines
while ($line = fgetcsv($f)){
$arrayToBeSorted[] = $line;
}
usort($arrayToBeSorted, 'my_sort');
function my_sort($lineA, $lineB){
// set this to the column that needs to be sorted
global $headings;
$linePartsA = explode(',' $lineA);
$linePartsB = explode(',' $lineB);
if ($linePartsA[$headings] == $linePartsB[$heading) return 0;
return ($linePartsA[$headings] > $linePartsB[$heading]) ? -1 : 1;
}
}

Answer 2

Why do you want to use php only . I used jquery table sorter which is very efficient .here is the link table sorter