How to filter array in powershell

Question

I have an array in Powershell with some strings, for example

$StringArray = {"all_srv_inf", "all_srv_inf_vir", "all_srv_inf_vir_vmw", "all_srv_rol", "all_srv_rol_iis", "all_srv_rol_dc"}

I would like to filter all strings in the array, so only the most unique ones are left over.

So, in the above example, I would have to filter "all_srv_inf", "all_srv_inf_vir" and "all_srv_rol" resulting in a string array with only these value: "all_srv_inf_vir_vmw", "all_srv_rol_iis" and "all_srv_rol_dc"

The list is actually a lot longer, so I what would be the most efficient way to filter my Powershell string array?

Thanks.

If the answer below helped you, please also consider upvoting it. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Sep 11, 2017 at 10:48

Frode F. · Accepted Answer · 2017-06-13 05:31:01Z

1

Your variable does not contain an actualy array, but rather a scriptblock that generates an array when invoked.

There are many ways to filter strings, which you can find by searching here on SO or Google. You could could try a few solutions using Measure-Command { #your code } to see how long it takes and compare the results.

My first two ideas would have been using -notmatch or -notcontains/-notin. -notmatch uses regex which are usually faster, so I would start with that. Another solution might peform better for you depending on you input data etc. so you should try different approaches and measure them.

Sample with -notmatch:

$StringArray = "all_srv_inf", "all_srv_inf_vir", "all_srv_inf_vir_vmw", "all_srv_rol", "all_srv_rol_iis", "all_srv_rol_dc"

#Build regex for items to exclude
$exclude = ('all_srv_inf', 'all_srv_inf_vir','all_srv_rol' | ForEach-Object { "^$([regex]::Escape($_))$" }) -join '|'

#Filter stringarray
$StringArray -notmatch $exclude

edited Jun 13, 2017 at 5:31

answered Jan 31, 2015 at 16:40

Frode F.

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willemdh Over a year ago

Thanks Frode. I promise you I did pu a lot of time in it. Created some functions to handle it, whuch went through the array and checked if the string was a substring of one of the string in the array. Anyway, your solution to put the 'top level' strings that had to be excluded in a seperate array works very fast. Thanks again.

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