Unique elements of an array with multiple criteria

Question

I have an array that has objects with multiple properties. I use two of them for sorting, eg name and a numeric value (descending):

Joe 120

Joe 111

Joe 89

Joe 45

Kyle 500

Kyle 300

Kyle 120

Kyle 60

etc.

I collect these from multiple sources, so have my array with similar count for each name.

I only need the first line for each name - the largest numeric value.

It is a fairly large data set with 60k lines. Tried to foreach through the whole with matching the list of users and selecting the first instance. Painfully slow

To set the numeric value in desc you need some trick:

$sorted = $array | Sort-Object Name, @{Name='Money';expression = {$_.Money};Ascending = $false }

However, unique switch would only work with one element. But if I do:

$sorted | Sort-Object -Property Name -Unique

this messes up the previous sort that used two criteria, so I am not getting the largest value for that username :(

Answer 1

I would use Group-Object for this and then select the highest numeric value from that result.

$array | Group-Object Name |
  Select-Object Name,@{n='Money';e={([int[]]$_.Group.Money | Sort-Object -Descending)[0]}}

Explanation:

Group-Object Name will create a unique entry for each original Name as a new property called Name . Each entry has a Group property that contains all objects that have the same Name value and the corresponding Money values.

Select-Object displays the Name property and a calculated Money property. The Money property takes the array of money values, casts them to type [int] , and then sorts in descending order. Since you only want the highest value, only the first element of the array [0] is selected.

Answer 2

Use a hashtable to hold the maximum value per Name value:

$maxValues = @{}

foreach($value in $array){
  if($maxValues[$value.Name] -ge $value.Money){
    # amount is smaller, skip updating
    continue
  }
  $maxValues[$value.Name] = [int]$value.Money
}

The $maxValues hashtable will now hold the maximum amount per name:

PS C:\> $maxValues

Name                           Value
----                           -----
Joe                            120
Kyle                           500