Does Powershell have an Aggregate/Reduce function? - powershell

Question

I realize there are related questions, but all the answers seem to be work-arounds that avoid the heart of the matter. Does powershell have an operation that can use a scriptblock to aggregate elements of an array into a single value? This is what is known in other languages as aggregate or reduce or fold.
I can write it myself pretty easily, but given that its the base operation of any list processing, I would assume there's something built in I just don't know about.
So what I'm looking for is something like this
1..10 | Aggregate-Array {param($memo, $x); $memo * $x}

Answer 1

There is not anything so obviously named as Reduce-Object but you can achieve your goal with Foreach-Object:
1..10 | Foreach {$total=1} {$total *= $_} {$total}
BTW there also isn't a Join-Object to merge two sequences of data based on some matching property.

Answer 2

If you need Maximum, Minimum, Sum or Average you can use Measure-Object sadly it dosen´t handle any other aggregate method.
Get-ChildItem | Measure-Object -Property Length -Minimum -Maximum -Average

Answer 3

This is something I wanted to start for a while. Seeing this question, just wrote a pslinq (https://github.com/manojlds/pslinq) utility. The first and only cmdlet as of now is Aggregate-List, which can be used like below:
1..10 | Aggregate-List { $acc * $input } -seed 1
#3628800
Sum:
1..10 | Aggregate-List { $acc + $input }
#55
String reverse:
"abcdefg" -split '' | Aggregate-List { $input + $acc }
#gfedcba
PS: This is more an experiment

Answer 4

Ran into a similar issue recently. Here's a pure Powershell solution. Doesn't handle arrays within arrays and strings like the Javascript version does but maybe a good starting point.
function Reduce-Object {
[CmdletBinding()]
[Alias("reduce")]
[OutputType([Int])]
param(
# Meant to be passed in through pipeline.
[Parameter(Mandatory=$True,
ValueFromPipeline=$True,
ValueFromPipelineByPropertyName=$True)]
[Array] $InputObject,
# Position=0 because we assume pipeline usage by default.
[Parameter(Mandatory=$True,
Position=0)]
[ScriptBlock] $ScriptBlock,
[Parameter(Mandatory=$False,
Position=1)]
[Int] $InitialValue
)
begin {
if ($InitialValue) { $Accumulator = $InitialValue }
}
process {
foreach($Value in $InputObject) {
if ($Accumulator) {
# Execute script block given as param with values.
$Accumulator = $ScriptBlock.InvokeReturnAsIs($Accumulator, $Value)
} else {
# Contigency for no initial value given.
$Accumulator = $Value
}
}
}
end {
return $Accumulator
}
}
1..10 | reduce {param($a, $b) $a + $b}
# Or
reduce -inputobject #(1,2,3,4) {param($a, $b) $a + $b} -InitialValue 2

Answer 5

There's a functional module I came upon https://github.com/chriskuech/functional that has a reduce-object, also merge-object, test-equality, etc. It's surprising that powershell has map (foreach-object) and filter (where-object) but not reduce. https://medium.com/swlh/functional-programming-in-powershell-876edde1aadb Even javascript has reduce for arrays. A reducer actually is very powerful. You can define map and filter in terms of it.
1..10 | reduce-object { $a * $b }
3628800
Measure-object can't sum [timespan]'s:
1..10 | % { [timespan]"$_" } | Reduce-Object { $a + $b } | ft
Days Hours Minutes Seconds Milliseconds
---- ----- ------- ------- ------------
55 0 0 0 0
Merge two objects:
#{a=1},#{b=2} | % { [pscustomobject]$_ } | Merge-Object -Strategy fail
b a
- -
2 1