PHPExcel deleting rows from large worksheet - php

Question

I am trying to delete rows based on conditions such as Cell B = 59/61. However, PHPExcel loads the rows very slowly. For a worksheet with 18000 rows/3MB, it takes around 4 hours 30 minutes to load. How can I improve the speed of the data worksheet to load and delete?
set_include_path(get_include_path() . PATH_SEPARATOR . 'Classes/');
/** PHPExcel_IOFactory */
include 'PHPExcel/IOFactory.php';
//Defining File Type
$fileType = "Excel2007";
//Retrieving File
$tmpfname = "bigfile.xlsx";
//Loading file into PHPExcel
$objPHPExcel = PHPExcel_IOFactory::load($tmpfname);
$worksheet = $objPHPExcel->getSheet(0); //Worksheet of file defined as first
$lastRow = $worksheet->getHighestRow();
//Determine which rows to be remove
$DeletedRows = [];
$DeletedRowCount = 0;
for ($row = 2; $row <= $lastRow; $row++) {
//Checker
$CellA = $worksheet->getCell('A' . $row)->getValue();
$CellB = $worksheet->getCell('B' . $row)->getValue();
$CellE = $worksheet->getCell('E' . $row)->getValue();
//To check condition
if ($CellB != 8 && $CellB != 9 && $CellB != 18 && $CellB != 19) {
$DeletedRows[] = $row;
continue;
}
//To check if condition
else if ($CellE == 59 || $CellE == 61){
$DeletedRows[] = $row;
continue;
}
}
//Removing the rows
//Deleting this way as when one row deleted, one row less.
foreach ($DeletedRows as $key => $value) {
$row = $value - $DeletedRowCount;
$objPHPExcel->getActiveSheet()->removeRow($row, 1);
$DeletedRowCount++;
}
//Write file into original file
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, $fileType);
$objWriter->save($tmpfname);

Answer 1

Well one way to improve performance is to work upwards from the bottom of the spreadsheet rather than downwards.
When you delete a row, PHPExcel has to check the cells in every row below it and adjust references in those cells if necessary. This is more efficient, with fewer checks/updates necessary when you work from the bottom of the worksheet upwards.
It's also a lot more efficient if you can delete more than one row at a time. If you need to delete rows 15, 16 and 17; then
$objPHPExcel->getActiveSheet()->removeRow(15, 3);
is 3x faster than
$objPHPExcel->getActiveSheet()->removeRow(15, 1);
$objPHPExcel->getActiveSheet()->removeRow(16, 1);
$objPHPExcel->getActiveSheet()->removeRow(17, 1);
So spending a bit of time evaluating your $DeletedRows array looking for ranges could be beneficial
Your code would also be a lot faster if, instead of building an array of row numbers to delete in the first loop and deleting them in the second, you deleted them in the first loop... 1 loop will inevitably be faster than 2 loops
Lastly, there is one major flaw with your approach. If your first loop tells you that you need to delete rows 1, 5; you delete row 1 and then 5.... except that row 5 is actually row 4 since you deleted row 1, and you've actually just deleted the row that was row 6 when you did your original loop to assess which rows to delete.... working from bottom to top would prevent this problem as well as being more efficient