Convert Excel column coordinates to integer position in PHP - php

Question

I need to convert Excel coordinates (for example "AD45") into X=30 and Y=45 positions in integers.
I have this snippet of PHP code:
/**
* #param String $coordinates
*
* #return array
*/
public function getCoordinatesPositions($coordinates) {
$letters = preg_replace('/[^a-zA-Z]/', '', $coordinates);
$numbers = preg_replace('/[^0-9]/', '', $coordinates);
$letters = strtoupper($letters);
$columnCoordinate = 0;
$alphabetIterate = 0;
$alphabetRange = range('A', 'Z');
$alphabetCount = count($alphabetRange);
$splittedLetters = str_split($letters);
$lettersCount = count($splittedLetters);
$i = 1;
if ($lettersCount === 1) {
$columnCoordinate = array_search($splittedLetters[0], $alphabetRange) + 1;
} else {
foreach ($splittedLetters as $letter) {
if ($i !== $lettersCount) {
$position = (array_search($letter, $alphabetRange) + 1) * $alphabetCount;
} else {
$position = (array_search($letter, $alphabetRange) + 1);
}
$columnCoordinate += $position;
$i++;
}
}
return array('column' => $columnCoordinate, 'row' => $numbers);
}
My problem is, that this function is not returning correct column value if you pass coordinates with 3 or more letters ("ABC45"). And my colleague said, that this algorithm is also poor performance.
Do you have any ideas for simpler and better performance algorithm? Thank you.

Answer 1

In principle the algorithm is fine. You can simplify it and make it more general this way:
function getCoordinatesPositions($coordinates) {
$letters = preg_replace('/[^a-zA-Z]/', '', $coordinates);
$numbers = preg_replace('/[^0-9]/', '', $coordinates);
$letters = strtoupper($letters);
$alphabetRange = range('A', 'Z');
$alphabetCount = count($alphabetRange);
$splittedLetters = str_split($letters);
$lettersCount = count($splittedLetters);
$columnCoordinate = 0;
$i = 1;
foreach ($splittedLetters as $letter) {
$columnCoordinate += (array_search($letter, $alphabetRange) + 1) * pow($alphabetCount, $lettersCount - $i);
$i++;
}
return array('column' => $columnCoordinate, 'row' => intval($numbers));
}
var_dump(getCoordinatesPositions("ABC456"));
For PHPExcel see PHPExcel how to get column index from cell.

Answer 2

The #Axel Richter's answer is a good solution and works fine, but it may be improved to:
Secure against wrong coordinates.
Reduce code.
And probably increase performance.
Here is the proposed version:
function getCoordinatesPositions($coordinates) {
if (preg_match('/^([a-z]+)(\d+)$/i', $coordinates, $matches)) {
$level = strlen($matches[1]);
$matches[1] = array_reduce(
str_split(strtoupper($matches[1])),
function($result, $letter) use (&$level) {
return $result + (ord($letter) - 64) * pow(26, --$level);
}
);
return array_splice($matches, 1);
}
// (returns NULL when wrong $coordinates)
}
Using the initial preg_match() ensures to avoid working with wrong coordinates, and directly extracts the column part into $matches['1'].
Now the main improvement is to use ord($letter) to compute the letter's individual value: it avoids creating a temporary array of range('A', 'Z'), and simplifies the evaluation.
Then array_reduce() allows more compact processing of the column part, which is modified in situ, so the final return is also simplified as a simple part of the intermediary $matches.