创建Powershell字典时，异常调用带有“ 2”参数的“添加”

Question

I'm trying to create a dictionary from the following file hostname.csv:

hostname        type
LON131          gaming
LON132          gaming
LON133          research
LON134          research

using the below Powershell script:

get-content hostname.csv | ForEach-Object {
    if ($dict.Keys -contains $_.type) {
        $dict[$_.type]+=$_.hostname
    } else {
        $dict.Add($_.type,@($_.hostname))
    }
}

Write-Host $dict;

But I keep getting the following error message:

Exception calling "Add" with "2" argument(s): "Key cannot be null.
Parameter name: key"
At fcheck.ps1:7 char:29
+         $dict.Add($_.type,@($_.hostname))
+                             ~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentNullException

Exception calling "Add" with "2" argument(s): "Key cannot be null.
Parameter name: key"
At fcheck.ps1:7 char:29
+         $dict.Add($_.type,@($_.hostname))
+                             ~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentNullException

Exception calling "Add" with "2" argument(s): "Key cannot be null.
Parameter name: key"
At fcheck.ps1:7 char:29
+         $dict.Add($_.type,@($_.hostname))
+                             ~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentNullException

Exception calling "Add" with "2" argument(s): "Key cannot be null.
Parameter name: key"
At fcheck.ps1:7 char:29
+         $dict.Add($_.type,@($_.hostname))
+                             ~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentNullException

Exception calling "Add" with "2" argument(s): "Key cannot be null.
Parameter name: key"
At fcheck.ps1:7 char:29
+         $dict.Add($_.type,@($_.hostname))
+                             ~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentNullException

What could be causing it and how do I go about resolving it?

Answer 1

"Key cannot be null." - $_.type does not evaluate to what is expected. ( Get-Content returns lines of text and doesn't know anything about CSV files/columns.)

The error message is misleading in that the problem has nothing to do with the number of arguments; this is just PowerShell providing some details about the dynamic method call.

In any case, barring the issue noted above, the Add could be rewritten as $dict[$_.type] = @($_.hostname) for uniformity. Of course the CSV data needs to be correctly read first.

Answer 2

You might try replacing get-content hostname.csv with:

Import-CSV -Delimiter "`t" -Path hostname.csv

EDIT:

I think you might not be initializing dict priro to calling $dict.keys . The following worked for me:

$dict = @{} 
Import-Csv -Path .\test.csv -Delimiter "`t" | ForEach-Object {
    if ($dict.Keys -contains $_.type) {
        $dict[$_.type]+=$_.hostname
    } else {
        $dict[$_.type] = @($_.hostname)
    }
}

$dict