Comparing 3 CSV Files and generating output to 4th One..

Question

Hi,
I was trying to compare 3 different CSV files using the common field EmplID and generate output with the combination of all the CSV's. The fields in the CSV are below
CSV1 : EmplID,HName,Name,PreferredName,Location,Department
CSV2 : HName,EmplID,first_name,last_name,email
CSV3 : Emplid,Extension
I would like to generate the output CSV as below..
OutputCSV :EmplID,Hname,Name,PreferredName,Location,Department,first_name,last_name,email,Extension
The below script works but as it is comparing the data by row by row, it takes huge time to complete.. Can anybody suggest how can i improve the performance of the same... 
$CSV1 = Import-CSV "Abc.CSV"
$CSV2 = Import-CSV "DEF.CSV"
$CSV3 = Import-CSV "GHI.CSV"
$Merged = ForEach($Record in $CSV1){
Add-Member -InputObject $Record -NotePropertyName 'first_name' -NotePropertyValue ($CSV2|Where{$_.EmplID -eq $Record.EmplID}|Select -Expand first_name)
Add-Member -InputObject $Record -NotePropertyName 'last_name' -NotePropertyValue ($CSV2|Where{$_.EmplID -eq $Record.EmplID}|Select -Expand last_name)
Add-Member -InputObject $Record -NotePropertyName 'email' -NotePropertyValue ($CSV2|Where{$_.EmplID -eq $Record.EmplID}|Select -Expand email)
Add-Member -InputObject $Record -NotePropertyName 'Extension' -NotePropertyValue ($CSV3|Where{$_.EmplID -eq $Record.EmplID}|Select -Expand Extension) -PassThru
$Merged | Export-CSV C:\Path\To\New.CSV -NoTypeInfo

Answer 1

Hi RP,
you can do this by creating a dictionary that uses the Employee ID as key. This allows you to iterate over each Csv only once and add values to the correct object each time. Didn't test it, but this ought to do the trick:
$CSV1 = Import-CSV "Abc.CSV"
$CSV2 = Import-CSV "DEF.CSV"
$CSV3 = Import-CSV "GHI.CSV"
$Hash = @{ }
foreach ($Record in $CSV1)
$Hash[$Record.EmplID] = $Record | Select EmplID, Hname, Name, PreferredName, Location, Department, first_name, last_name, email, Extension
foreach ($Record in $CSV2)
try
$Hash[$Record.EmplID].first_name = $Record.first_name
$Hash[$Record.EmplID].last_name = $Record.last_name
$Hash[$Record.EmplID].email = $Record.email
catch
Write-Warning "[Csv2]Failed to process $($Record.emplID): $($_.Exception.Message)"
foreach ($Record in $CSV3)
try
$Hash[$Record.EmplID].Extension = $Record.Extension
catch
Write-Warning "[Csv3]Failed to process $($Record.emplID): $($_.Exception.Message)"
$Hash.Values | Export-CSV C:\Path\To\New.CSV -NoTypeInfo
Cheers,
Fred
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