New-FastLookup.ps1
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function New-FastLookup { <# .SYNOPSIS Lookup a value in an array faster than Where-Object .DESCRIPTION Improve the speed of looking up a value in an array by creating a hashtable index. Good for looking up results in very large arrays or CSV files (e.g Import-Csv) .NOTES Version: 1.0 Author: Miles Gratz Creation Date: April 10, 2017 Purpose/Change: Initial script development .PARAMETER Array A mandatory parameter specifying input array used to create 'FastLookup' .PARAMETER Header An optional parameter specifying the header in the input array used to create 'FastLookup' .OUTPUTS A hashtable, listing the values in the array and their corresponding index .EXAMPLE PS> $array = 1..10000000 PS> $hashtable = New-FastLookup $array PS> Measure-Command { $array | Where-Object { $_ -eq 199999 } } Days : 0 Hours : 0 Minutes : 0 Seconds : 9 Milliseconds : 306 PS> Measure-Command { Get-FastLookup -Value 199999 -Array $array -Table $hashtable } Days : 0 Hours : 0 Minutes : 0 Seconds : 0 Milliseconds : 65 [NOTE] Performance test on Windows 10 x64 (i5-6200U, 8GB RAM, SSD) #> param( [Parameter(Mandatory=$true)] [array]$Array, $Header ) # Identify headers in input array $Headers = $Array | Get-Member -MemberType 'NoteProperty' | Select-Object -ExpandProperty 'Name' # Define empty hashtable and index $HashTable = @{} $Index = 0 #1: Header specified #2: Header exists in array If (($Header -ne $null) -and ($Header -in $Headers)) { # Redefine array with only data from specified Header $Array = $Array.$Header } #1: Header is specified #2: Header does NOT exist in array ElseIf (($Header -ne $null) -and ($Header -notin $Headers)) { # Exit function with error Write-Error "Specified header ($Header) does not exist in input array." Break } #1: Header is NOT specified #2: Array contains multiple Headers ElseIf (($Header -eq $null) -and ($Headers.Count -gt 1)) { # Exit function with error Write-Error "Input array requires the -Header parameter (multiple columns detected)." Break } # Loop through array foreach ($Item in $Array) { # Add index of Item to hashtable # Name Value # ---- ----- # Server1 953 # Server2 1157 Try { $HashTable.Add($Item,$Index) } # Duplicate key detected, add to existing value # Name Value # ---- ----- # Server1 953 # Server2 1157,3325 Catch { $HashTable[$Item] = ($HashTable[$Item],$Index -join ",") } # Increment loop $Index++ } # Output results $HashTable } |