Powershell 基于一个对象创建一个新的对象数组，其中某些项目将被删除

Question

I am trying to create a new array based on some rules I have to follow. I am sure there is some easier way to do this but I cannot figure it out!

$files array contains the following:

Name                   Amount
-----------            --------------
KL                     3
KS                     55
KS                     54
KS                     50
KM                     4
KD                     1
KW                     4
KD                     3
KV                     4
KD                     4
KL                     7
KS                     1

I want to create a new array in the same order as the above, but remove all but the latest KD & KL name. Which would look like:

    KS                     55
KS                     54
KS                     50
KM                     4
KW                     4
KV                     4
KD                     4
KL                     7
KS                     1

So far I have been trying to forloop to work out the amount of KD & KL's but I am getting confused with how to just add the ones later in the list.

Answer 1

Use an ordered dictionary to keep track of the last seen object with a given name:

$latest = [ordered]@{}

$files |ForEach-Object {
  $latest[$_.Name] = $_
}

$arrayWithOnlyLatest = $latest.Values

$arrayWithOnlyLatest now contains only the last seen objects with each name

Answer 2

I'm sure there is a much more clever way, but instead of getting the last KD/KL, you could just do the opposite. Reverse the array, only keep the first KD/KL, then reverse the array back.

[array]::Reverse($files)

$kdfound = $klfound = $false

$files = switch -Regex ($files)
{
    'KD' {if($kdfound -eq $false){$kdfound = $true; $_}}
    'KL' {if($klfound -eq $false){$klfound = $true; $_}}
    default {$_}
}

[array]::Reverse($files)

$files

Output

Name,Amount
KS,55
KS,54
KS,50
KM,4
KW,4
KV,4
KD,4
KL,7
KS,1