PowerShell - filtering for unique values - powershell

Question

I have an input CSV file with a column containing information similar to the sample below:
805265
995874
805674
984654
332574
339852
I'd like to extract unique values into a array based on the leading two characters, so using the above sample my result would be:
80, 99, 98, 33
How might I achieve this using PowerShell?

Answer 1

Use Select-Object and parameter -unique:
$values =
'805265',
'995874',
'805674',
'984654',
'332574',
'339852'
$values |
Foreach-Object { $_.Substring(0,2) } |
Select-Object -unique
If conversion to int is needed, then just cast it to [int]:
$ints =
$values |
Foreach-Object { [int]$_.Substring(0,2) } |
Select-Object -unique

Answer 2

I'd use the Group-Object cmdlet (alias group) for this:
Import-Csv foo.csv | group {$_.ColumnName.Substring(0, 2)}
Count Name Group
----- ---- -----
2 80 {805265, 805674}
1 99 {995874}
1 98 {984654}
2 33 {332574, 339852}

Answer 3

You might use a hash table:
$values = #(805265, 995874, 805674, 984654, 332574, 339852)
$ht = #{}
$values | foreach {$ht[$_ -replace '^(..).+','$1']++}
$ht.keys
99
98
33
80

Answer 4

You could make a new array with items containing the first two characters and then use Select-Object to give you the unique items like this:
$newArray = #()
$csv = Import-Csv -Path C:\your.csv
$csv | % {
$newArray += $_.YourColumn.Substring(0, 2)
}
$newArray | Select-Object -Unique

Answer 5

Just another option instead of using Select-Object -unique would be to use the Get-Unique cmdlet (or its alias gu; see the detailed description here) as demonstrated below:
$values = #(805265, 995874, 805674, 984654, 332574, 339852)
$values | % { $_.ToString().Substring(0,2) } | Get-Unique
# Or the same using the alias
$values | % { $_.ToString().Substring(0,2) } | gu