Powershell: Setting values of a filtered array

Question

Hi All

I want to read in a csv file, filter it based on the values of two of the fields and set the value of another field. Here's a simple example of what I'm trying to achieve:

c:\somefile.csv contents:

firstField,secondField,thirdField
1,2,"somevalue"
2,2,"avalue"
3,1,"somevalue"

#Import file into array
$csv = Import-Csv c:\somefile.csv

# Where secondField = 2 and thirdField = "someValue" set thirdField =
"anotherValue"
$csv | where {$_secondField -eq 2 -and $_.thirdField = "somevalue"} |
<set value of thirdField = "anotherValue">

How can I do this. As you can see, from the example about, I can read in and filter the array. But I don't know how to then set the value of the thirdField. I tried set-itemproperty but got the error: "The WriteObject and WriteError methods cannot be called after the pipeline has been closed".

Edit: I would also only like to change to value of the first 2 items (rows) returned. Answered by me: I used Select -first 2.

Any advice on how to achive this would be appreciated.

Alan T

Answer 1

I altered your code a little bit:

$csv | 
    Where-Object {$_.secondField -eq 2 -and $_.thirdField -eq 'somevalue'} |
    Foreach-Object { $_.thirdField = 'anotherValue' }

• $_secondField => $_.secondField
• $_.thirdField = "somevalue" should be $_.thirdField -eq "somevalue"
• Foreach-Object sets the third value. It processes only 1 record in this case, but basically it processes all the records that are piped in (just try to remove the Where part).
• it is 'safer' to use single quote instead of double quote because of unintended variable expansion.

Answer 2

You've got the right idea. Use Where-Object (aliased to Where) to filter the objects in the pipeline and then further down the pipeline use Foreach-Object (aliased to Foreach) to set the value like so:

$csv | where {$_secondField -eq 2 -and $_.thirdField -eq "somevalue"} | 
    foreach {$_.thirdField = "notherValue"}

Think of Where-Object as just a filter mechanism and Foreach-Object as the pipeline mechanism that allows you to apply arbitrary script to each pipeline object.