What's the best way in PowerShell to parse these strings?

Question

I'm getting two string passed into my script:

"Project1,Project2,Project3,Project4"
"web,batch,web,components"

The strings come from a tool in our DevOps toolchain and I have no control over the input format. String 1 could be any number of projects. String 2 will be the same number of entries with the "type" of the project in string 1.

I need to emit one string for each distinct type in the second string that contains the projects from the first string:

"Project1,Project3"
"Project2"
"Project4"

I know I can do it with a bunch of nested foreach loops. Is there a way to do this with a hashtable and/or arrays?

Answer 1

You can turn the original input strings into arrays with the -split operator:

$ProjectNames = "Project1,Project2,Project3,Project4" -split ','
$ProjectTypes = "web,batch,web,components" -split ','

Then create an empty hash table to contain the type-to-projectname mappings

$ProjectsByType = @{}

Finally iterate over the two arrays to group the project names by type:

for($i = 0; $i -lt $ProjectNames.Count; $i++){
    if(-not $ProjectsByType.ContainsKey($ProjectTypes[$i])){
        # Create key and entry as array if it doesn't already exist
        $ProjectsByType[$ProjectTypes[$i]] = @()
    }
    # Add the project to the appropriate project type key
    $ProjectsByType[$ProjectTypes[$i]] += $ProjectNames[$i]
}

Now you can produce your desired strings grouped by project type:

$ProjectsByType.Keys |ForEach-Object {
    $ProjectsByType[$_] -join ','
}

---

You could also create objects from the two arrays and use Group-Object to group them:

$Projects = for($i = 0; $i -lt $ProjectNames.Count; $i++){
    New-Object psobject -Property @{
        Name = $ProjectNames[$i]
        Type = $ProjectTypes[$i]
    }
}

$Projects |Group-Object -Property Type

This is more interesting if you want to do further processing of the projects, if you just need the strings the first approach is easier

Answer 2

There isn't really an elegant way of combining two arrays that way with built-in methods. A somewhat convoluted way would be the following:

$projects = $projectString -split ','
$types = $typeString -split ','
0..($projects.Count) | group { $types[$_] } | % { $projects[$_.Group] -join ',' }

However, this first generates indices into the arrays to group and format them later, which is inherently a bit iffy (and not very understandable). I tend to pre-process the data to actually reflect what I'm operating on:

$projects = $projectString -split ','
$types = $typeString -split ','
$projectsWithType = 0..($projects.Count) | % {
  [pscustomobject]@{
    Project = $projects[$_]
    Type = $types[$_]
  }
}
$projectsWithType | group Type | % { $_.Group -join ',' }

This makes the actual data munging task much clearer.

Answer 3

with only one search in first list

$projects = "Project1,Project2,Project3,Project4" -split ','
$types = "web,batch,web,components" -split ','

$linenumber = 0

$projects |%{New-Object psObject -Property @{Project=$_;TypeProject= $types[$linenumber]};$linenumber++} |
group TypeProject |
select Name, @{N="Projects";E={$_.Group.Project -join ","}}