Improve Performance of Csv Writer

Fix #3904. PR #3839 provided a huge performance boost for sparsely populated spreadsheets. Unfortunately, it degraded performance for more densely populated spreadsheets when writing Csvs. The reason is that Csv Writer calls toArray for each row, meaning that a lot of the intermediate data used to speed things up needs to be recalculated for every row. It would be better off calling toArray just once for the entire spreadsheet; however this gives back some of the memory improvements of PR #3834. However, the memory effects can be substantially alleviated by supplying a Generator function to do the work. This PR does that; the result is that Csv Writer is now quite a bit faster, and with only a small memory uptick, vs. its performance in PhpSpreadsheet 1.29.

src/PhpSpreadsheet/Worksheet/Worksheet.php

@@ -3,6 +3,7 @@
 namespace PhpOffice\PhpSpreadsheet\Worksheet;
 
 use ArrayObject;
+use Generator;
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
 use PhpOffice\PhpSpreadsheet\Cell\AddressRange;
@@ -2800,9 +2801,6 @@ class Worksheet implements IComparable
         return $returnValue;
     }
 
-    /** @var array<string, bool> */
-    private array $hiddenColumns;
-
     /**
      * Create array from a range of cells.
      *
@@ -2822,9 +2820,40 @@ class Worksheet implements IComparable
         bool $returnCellRef = false,
         bool $ignoreHidden = false
     ): array {
+        $returnValue = [];
+
+        // Loop through rows
+        foreach ($this->rangeToArrayYieldRows($range, $nullValue, $calculateFormulas, $formatData, $returnCellRef, $ignoreHidden) as $rowRef => $rowArray) {
+            $returnValue[$rowRef] = $rowArray;
+        }
+
+        // Return
+        return $returnValue;
+    }
+
+    /**
+     * Create array from a range of cells, yielding each row in turn.
+     *
+     * @param mixed $nullValue Value returned in the array entry if a cell doesn't exist
+     * @param bool $calculateFormulas Should formulas be calculated?
+     * @param bool $formatData Should formatting be applied to cell values?
+     * @param bool $returnCellRef False - Return a simple array of rows and columns indexed by number counting from zero
+     *                             True - Return rows and columns indexed by their actual row and column IDs
+     * @param bool $ignoreHidden False - Return values for rows/columns even if they are defined as hidden.
+     *                            True - Don't return values for rows/columns that are defined as hidden.
+     *
+     * @return Generator
+     */
+    public function rangeToArrayYieldRows(
+        string $range,
+        mixed $nullValue = null,
+        bool $calculateFormulas = true,
+        bool $formatData = true,
+        bool $returnCellRef = false,
+        bool $ignoreHidden = false
+    ) {
         $range = Validations::validateCellOrCellRange($range);
 
-        $returnValue = [];
         //    Identify the range that we need to extract from the worksheet
         [$rangeStart, $rangeEnd] = Coordinate::rangeBoundaries($range);
         $minCol = Coordinate::stringFromColumnIndex($rangeStart[0]);
@@ -2835,8 +2864,10 @@ class Worksheet implements IComparable
         $maxColInt = $rangeEnd[0];
 
         ++$maxCol;
-        $nullRow = $this->buildNullRow($nullValue, $minCol, $maxCol, $returnCellRef, $ignoreHidden);
-        $hideColumns = !empty($this->hiddenColumns);
+        /** @var array<string, bool> */
+        $hiddenColumns = [];
+        $nullRow = $this->buildNullRow($nullValue, $minCol, $maxCol, $returnCellRef, $ignoreHidden, $hiddenColumns);
+        $hideColumns = !empty($hiddenColumns);
 
         $keys = $this->cellCollection->getSortedCoordinatesInt();
         $keyIndex = 0;
@@ -2847,7 +2878,7 @@ class Worksheet implements IComparable
                 continue;
             }
             $rowRef = $returnCellRef ? $row : ($row - $minRow);
-            $returnValue[$rowRef] = $nullRow;
+            $returnValue = $nullRow;
 
             $index = ($row - 1) * AddressRange::MAX_COLUMN_INT + 1;
             $indexPlus = $index + AddressRange::MAX_COLUMN_INT - 1;
@@ -2860,24 +2891,22 @@ class Worksheet implements IComparable
                 $thisCol = ($key % AddressRange::MAX_COLUMN_INT) ?: AddressRange::MAX_COLUMN_INT;
                 if ($thisCol >= $minColInt && $thisCol <= $maxColInt) {
                     $col = Coordinate::stringFromColumnIndex($thisCol);
-                    if ($hideColumns === false || !isset($this->hiddenColumns[$col])) {
+                    if ($hideColumns === false || !isset($hiddenColumns[$col])) {
                         $columnRef = $returnCellRef ? $col : ($thisCol - $minColInt);
                         $cell = $this->cellCollection->get("{$col}{$thisRow}");
                         if ($cell !== null) {
                             $value = $this->cellToArray($cell, $calculateFormulas, $formatData, $nullValue);
                             if ($value !== $nullValue) {
-                                $returnValue[$rowRef][$columnRef] = $value;
+                                $returnValue[$columnRef] = $value;
                             }
                         }
                     }
                 }
                 ++$keyIndex;
             }
-        }
-        unset($this->hiddenColumns);
 
-        // Return
-        return $returnValue;
+            yield $rowRef => $returnValue;
+        }
     }
 
     /**
@@ -2890,6 +2919,7 @@ class Worksheet implements IComparable
      *                              True - Return rows and columns indexed by their actual row and column IDs
      * @param bool $ignoreHidden False - Return values for rows/columns even if they are defined as hidden.
      *                             True - Don't return values for rows/columns that are defined as hidden.
+     * @param array<string, bool> $hiddenColumns
      */
     private function buildNullRow(
         mixed $nullValue,
@@ -2897,13 +2927,13 @@ class Worksheet implements IComparable
         string $maxCol,
         bool $returnCellRef,
         bool $ignoreHidden,
+        array &$hiddenColumns
     ): array {
-        $this->hiddenColumns = [];
         $nullRow = [];
         $c = -1;
         for ($col = $minCol; $col !== $maxCol; ++$col) {
             if ($ignoreHidden === true && $this->columnDimensionExists($col) && $this->getColumnDimension($col)->getVisible() === false) {
-                $this->hiddenColumns[$col] = true;
+                $hiddenColumns[$col] = true;
             } else {
                 $columnRef = $returnCellRef ? $col : ++$c;
                 $nullRow[$columnRef] = $nullValue;

src/PhpSpreadsheet/Writer/Csv.php

@@ -104,11 +104,8 @@ class Csv extends BaseWriter
         $maxRow = $sheet->getHighestDataRow();
 
         // Write rows to file
-        for ($row = 1; $row <= $maxRow; ++$row) {
-            // Convert the row to an array...
-            $cellsArray = $sheet->rangeToArray('A' . $row . ':' . $maxCol . $row, '', $this->preCalculateFormulas);
-            // ... and write to the file
-            $this->writeLine($this->fileHandle, $cellsArray[0]);
+        foreach ($sheet->rangeToArrayYieldRows("A1:$maxCol$maxRow", '', $this->preCalculateFormulas) as $cellsArray) {
+            $this->writeLine($this->fileHandle, $cellsArray);
         }
 
         $this->maybeCloseFileHandle();