how to use "if" statements inside pipeline

Question

I'm trying to use if inside a pipeline.

I know that there is where (alias ?) filter, but what if I want activate a filter only if a certain condition is satisfied?

I mean, for example:

get-something | ? {$_.someone -eq 'somespecific'} | format-table

How to use if inside the pipeline to switch the filter on/off? Is it possible? Does it make sense?

Thanks

EDITED to clarify

Without pipeline it would look like this:

if($filter) {
 get-something | ? {$_.someone -eq 'somespecific'}
}
else {
 get-something
}

EDIT after ANSWER's riknik

Silly example showing what I was looking for. You have a denormalized table of data stored on a variable $data and you want to perform a kind of "drill-down" data filtering:

function datafilter {
param([switch]$ancestor,
    [switch]$parent,
    [switch]$child,
    [string]$myancestor,
    [string]$myparent,
    [string]$mychild,
    [array]$data=[])

$data |
? { (!$ancestor) -or ($_.ancestor -match $myancestor) } |
? { (!$parent) -or ($_.parent -match $myparent) } |
? { (!$child) -or ($_.child -match $mychild) } |

}

For example, if I want to filter by a specific parent only:

datafilter -parent -myparent 'myparent' -data $mydata

That's very elegant, performant and simple way to exploit ?. Try to do the same using if and you will understand what I mean.

I think you mean to write: get-something | ? { $_.someone -eq 'somespecific' } | format-table You have ( and ) instead of { and }. — x0n, Apr 28 '11 at 15:04
See http://stackoverflow.com/a/20123883/223837 for another answer. — MarnixKlooster ReinstateMonica, Nov 21 '13 at 16:11

score 15 · Accepted Answer · answered Apr 27 '11 at 21:06

15

When using where-object, the condition doesn't have to strictly be related to the objects that are passing through the pipeline. So consider a case where sometimes we wanted to filter for odd objects, but only if some other condition was met:

$filter = $true
1..10 | ? { (-not $filter) -or ($_ % 2) }

$filter = $false
1..10 | ? { (-not $filter) -or ($_ % 2) }

Is this kind of what you are looking for?

answered Apr 27 '11 at 21:06

Daniel Richnak

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8
12

Hi, reading your answer more carefully and trying some silly test, I've found it useful. Thanks. I'm going to edit my original question inserting some clarification on how such a logic can be used. – Emiliano Poggi Apr 28 '11 at 15:55
Cool, glad it could help. It's nice and compact, if a bit unclear on what it's doing. :) I now understand a bit more about what you're trying to do, now that I see that you want to chain multiple potential filters in the pipeline. Neat idea. :) – Daniel Richnak Apr 28 '11 at 20:57
Nice. I used this approach when filtering values when a parameter was supplied, while ignoring the filter if the parameter wasn't supplied: `Where-Object { -not $Path -or $_.Path -like $Path }` – craig Feb 21 '18 at 22:26

score 3 · Answer 2 · answered Apr 28 '11 at 07:40

3

Have you tried creating your own filter. (A silly) example:

filter MyFilter {
   if ( ($_ % 2) -eq 0) { Write-Host $_ }
   else { Write-Host ($_ * $_) }
}

PS> 1,2,3,4,5,6,7,8,9 | MyFilter
1
2
9
4
25
6
49
8
81

answered Apr 28 '11 at 07:40

Torbjörn Bergstedt

3,359
2
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30

Thanks, however in your example there is no way to command filtering. – Emiliano Poggi Apr 28 '11 at 13:01
1

Not sure what you mean, but you can have parameters to filters just like to a function. That way you get better control over how the filter works. – Torbjörn Bergstedt Apr 29 '11 at 06:55

Nicola Cossu · Answer 3 · 2011-04-27T20:15:56.040

2

I don't know if my answer can help you but I try :)

1..10 | % {if ($_ % 2 -eq 0) {$_}}

as you can see I use a loop and for each number between 1 and 10 I check if is even and I display it only in this case.

edited Apr 27 '11 at 20:15

answered Apr 27 '11 at 20:02

Nicola Cossu

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Thanks but it looks like a filter `1..10 | ? {($_ % 2) -eq 0}` – Emiliano Poggi Apr 27 '11 at 20:39
I'm afraid I don't understand your question then. Sorry. – Nicola Cossu Apr 27 '11 at 20:53
What does % in '% {...}' mean please? Thanks. – NoChance Sep 23 '16 at 21:46
@NoChance et al, it's shorthand for `Foreach-Object`, [more here](https://ss64.com/ps/foreach-object.html). – Aaron May 31 '19 at 01:16

how to use "if" statements inside pipeline

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