How to find the index of an element in an array by its value using Powershell

Question

I have an array of custom objects in Powershell. Each object has a unique reference with which it can be looked up in the array and a value I wish to use later which is not necessarily unique. The array is populated in a for loop as below

#Create empty array
$array1 = @()

#Populate array
foreach($otherElement in $otherArray){
  #Create custom array element
  $arrayElement = New-Object PSObject

  #Update Credential element   
  $arrayElement | Add-Member -type NoteProperty -Name 'objRef' -Value $($otherElement.getAttribute("ref") )
  $arrayElement | Add-Member -type NoteProperty -Name 'objValue' -Value $($otherElement.getAttribute("someValue") )

  #Add element to array
  $array1 += $arrayElement
}

After building the array I want to get access to the objValue corresponding to the correct objRef in some way. I know that you can test if an array contains a value using the -contains parameter but I don't know how to get the index of the object with that value.

Basically this array is acting like a look up table. I want a function to put in an objRef to get out an objValue.

The objValue in this case is a System.Management.Automation.PSCredential, the password for each object is input at runtime for security. At work I have to sometimes install the same software 30 odd times on different machines with the same 5 credentials and figuring this out will help me automate the process reomtely.

Thanks in advance!

If it's "acting" as a lookup, why don't you just use an actual lookup, as in, a hashtable (@{})? — Jeroen Mostert
– Jeroen Mostert, Commented Jun 16, 2016 at 12:23
Good question. I will look up hash tables and get back to you! — Flash_Steel
– Flash_Steel, Commented Jun 16, 2016 at 12:29
Thanks, Jeroen. That works like a charm while I have reference and value pairs. More generally, do you know of any functions which can return the indices of an element of an array which equals a certain value in Powershell? — Flash_Steel
– Flash_Steel, Commented Jun 16, 2016 at 12:41

Jeroen Mostert · Accepted Answer · 2016-06-16 12:48:27Z

8

PowerShell is .NET based, so everything arrays in .NET can do, they can do in PowerShell. In particular, since they implement IList, they have the .IndexOf method: @(10, 4, 6).indexof(6) returns 2.

Of course, in your particular case a hash table is more appropriate, since looking up values there is constant time while searching through an array takes linear time. This matters little in the case of small arrays, but adds up quickly if you're doing things in a loop.

answered Jun 16, 2016 at 12:48

Jeroen Mostert

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2 Comments

Flash_Steel Over a year ago

Thanks. I didn't realise that Powershell Arrays are .NET arrays (learning on the job...). Searching online for "Powershell Array" etc usually brought up tons of pages explaining just the very basics.

Peter M. Over a year ago

If the array contains strings case sensitivity might be an issue. Since IndexOf is case sensitive I had to include a ForEach{] method that every array owns since version 4.0 of PowerShell: $array1.ForEach{$_.ToLower()}.IndexOf("term")

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