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Fixes inefficient array usage in Import-Excel #1703

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Fixes inefficient array usage in Import-Excel #1703

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4 changes: 2 additions & 2 deletions Public/Import-Excel.ps1
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Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,7 @@
}

$targetSheetname = $sheet.Name
$xlBook["$targetSheetname"] = @()
$xlBook["$targetSheetname"] = [System.Collections.Generic.List[object]]::new()
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Copilot AI May 27, 2025

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Consider preallocating the list capacity if the expected number of rows can be estimated to further optimize performance and reduce potential reallocations.

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$xlBook["$targetSheetname"] = [System.Collections.Generic.List[object]]::new()
$rowCount = $sheet.Dimension.End.Row - $StartRow + 1
$xlBook["$targetSheetname"] = [System.Collections.Generic.List[object]]::new($rowCount)

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@scriptingstudio scriptingstudio May 27, 2025 •
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Hmm, good suggestion. Never thought of it.

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@scriptingstudio scriptingstudio May 27, 2025

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made some tests using preallocating. no difference

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@dfinke dfinke May 28, 2025

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just a thought, back in the Visual Basic days, before classes. When you did a ReDim on an already allocated array, we found that it was better to allocate 50% more than the size of the array as you went. Size 10, use it the ReDim to 15 not 11. Then 22, 33 and so on. Very effective.

No clue if that can play here.

#region Get rows and columns
#If we are doing dataonly it is quicker to work out which rows to ignore before processing the cells.
if (-not $EndRow ) { $EndRow = $sheet.Dimension.End.Row }
Expand Down Expand Up @@ -235,7 +235,7 @@
# Write-Verbose "Import cell '$($Worksheet.Cells[$R, $P.Column].Address)' with property name '$($p.Value)' and value '$($Worksheet.Cells[$R, $P.Column].Value)'."
}
}
$xlBook["$targetSheetname"] += [PSCustomObject]$NewRow
$xlBook["$targetSheetname"].Add([PSCustomObject]$NewRow)
}
#endregion
}
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