Analysis/Measure-VectorSimilarity.ps1
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function Measure-VectorSimilarity { <# .SYNOPSIS Measures the vector / cosine similarity between two sets of items. See: https://en.wikipedia.org/wiki/Cosine_similarity .EXAMPLE PS > .\Measure-VectorSimilarity.ps1 @(1..10) @(3..8) 0.775 .EXAMPLE PS > $items = dir c:\windows\ | Select -First 10 PS > $items2 = dir c:\windows\ | Select -First 8 PS > .\Measure-VectorSimilarity.ps1 $items $items2 -KeyProperty Name -ValueProperty Length 0.894 #> [CmdletBinding()] param( ## The first set of items to compare [Parameter(Position = 0)] $Set1, ## The second set of items to compare [Parameter(Position = 1)] $Set2, ## If the item sets represent objects that have a main property ## (like file names), the name of that key property [Parameter()] $KeyProperty, ## If the item sets represent objects that have a main property ## to represent the values (like Count or Percent), ## the name of that key property. If they don't have a property ## like this, simple existence of the item will be used. [Parameter()] $ValueProperty ) ## If either set is empty, there is no similarity if((-not $Set1) -or (-not $Set2)) { return 0 } ## Figure out the unique set of items to be compared - either based on ## the key property (if specified), or the item value directly $allkeys = @($Set1) + @($Set2) | Foreach-Object { if($PSBoundParameters.ContainsKey("KeyProperty")) { $_.$KeyProperty } else { $_ } } | Sort-Object -Unique ## Figure out the values of items to be compared - either based on ## the value property (if specified), or the item value directly. Put ## these into a hashtable so that we can process them efficiently. $set1Hash = @{} $set2Hash = @{} $setsToProcess = @($Set1, $Set1Hash), @($Set2, $Set2Hash) foreach($set in $setsToProcess) { $set[0] | Foreach-Object { if($PSBoundParameters.ContainsKey("ValueProperty")) { $value = $_.$ValueProperty } else { $value = 1 } if($PSBoundParameters.ContainsKey("KeyProperty")) { $_ = $_.$KeyProperty } $set[1][$_] = $value } } ## Calculate the vector / cosine similarity of the two sets ## based on their keys and values. $dot = 0 $mag1 = 0 $mag2 = 0 foreach($key in $allkeys) { $dot += $set1Hash[$key] * $set2Hash[$key] $mag1 += ($set1Hash[$key] * $set1Hash[$key]) $mag2 += ($set2Hash[$key] * $set2Hash[$key]) } $mag1 = [Math]::Sqrt($mag1) $mag2 = [Math]::Sqrt($mag2) ## Return the result [Math]::Round($dot / ($mag1 * $mag2), 3) } |