Adding objects to an array in a hashtable

Question

I want to create a Hashtable which groups files with the same name in arrays so I can later on work with those to list some properties of those files, like the folders where they're stored.

$ht = @{}
gci -recurse -file | % {
    try{
        $ht.Add($_.Name,@())
        $ht[$_.Name] += $_
    }
    catch{
        $ht[$_.Name] += $_
    }
}

All I'm getting is:

Index operation failed; the array index evaluated to null.
At line:8 char:13
+             $ht[$_.Name] += $_
+             ~~~~~~~~~~~~~~~~~~

I'm not sure why this isn't working, I'd appreciate any help.

if ($ht[$_.name]) { $ht[$_.name] += $_ } else { $ht[$_.name] = ,$_ } — woxxom
– woxxom, Commented Apr 23, 2017 at 19:28

Martin Brandl · Accepted Answer · 2017-04-23 20:02:30Z

2

Don't reinvent the wheel. You want to group files with the same name, use the Group-Object cmdlet:

$groupedFiles = Get-ChildItem -recurse -file | Group-Object Name

Now you can easy retrieve all file names that are present at least twice using the Where-Object cmdlet:

$groupedFiles | Where-Object Count -gt 1

You are getting this error because if your code hits the catch block, the current pipeline variable ($_) represents the last error and not the current item. You can fix that by either storing the current item an a variable, or you use the -PipelineVariable advanced cmdlet parameter:

$ht = @{}
gci -recurse -file -PipelineVariable item | %  {
    try{
        $ht.Add($item.Name,@())
        $ht[$item.Name] += $item
    }
    catch{
        $ht[$item.Name] += $item
    }
}

edited Apr 23, 2017 at 20:02

answered Apr 23, 2017 at 19:36

Martin Brandl

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