Move elements in an array of hashtables to another array in PowerShell

Question

I'd like to move hashtables from one array to another.

Assuming that I have an array of hashtables:

PS> $a = @( @{s='a';e='b'}, @{s='b';e='c'}, @{s='b';e='d'} )

Name                           Value
----                           -----
s                              a
e                              b
s                              b
e                              c
s                              b
e                              d

I can copy a selected set to another array:

PS> $b = $a | ? {$_.s -Eq 'b'}

Name                           Value
----                           -----
s                              b
e                              c
s                              b
e                              d

Then remove b's items from a:

PS> $a = $a | ? {$b -NotContains $_}

Name                           Value
----                           -----
s                              a
e                              b

Is there a more-succinct way of doing this?

beatcracker · Accepted Answer · 2016-05-17 18:54:27Z

3

PS 4.0 using Where method:

$b, $a = $a.Where({$_.s -Eq 'b'}, 'Split')

More info:

ForEach and Where magic methods

edited May 17, 2016 at 18:54

answered May 17, 2016 at 16:29

beatcracker

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1 Comment

craig Over a year ago

That's pretty slick.

Ansgar Wiechers · Accepted Answer · 2016-05-17 16:11:16Z

I would argue that doing two assignments with a filter and the inverted filter is the most straightforward way of doing this in PowerShell:

$b = $a | ? {$_.s -eq 'b'}       # x == y
$a = $a | ? {$_.s -ne 'b'}       # x != y, i.e. !(x == y)

You could wrap a function around this operation like this (using call by reference):

function Move-Elements {
  Param(
    [Parameter(Mandatory=$true)]
    [ref][array]$Source,
    [Parameter(Mandatory=$true)]
    [AllowEmptyCollection()]
    [ref][array]$Destination,
    [Parameter(Mandatory=$true)]
    [scriptblock]$Filter
  )

  $inverseFilter = [scriptblock]::Create("-not ($Filter)")

  $Destination.Value = $Source.Value | Where-Object $Filter
  $Source.Value      = $Source.Value | Where-Object $inverseFilter
}

$b = @()
Move-Elements ([ref]$a) ([ref]$b) {$_.s -eq 'b'}

or like this (returning a list of arrays):

function Remove-Elements {
  Param(
    [Parameter(Mandatory=$true)]
    [array]$Source,
    [Parameter(Mandatory=$true)]
    [scriptblock]$Filter
  )

  $inverseFilter = [scriptblock]::Create("-not ($Filter)")

  $destination = $Source | Where-Object $Filter
  $Source      = $Source | Where-Object $inverseFilter

  $Source, $destination
}

$a, $b = Remove-Elements $a {$_.s -eq 'b'}

or a combination of the above.

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