PS: Filter selected rows with only max values as output?

Question

I have a variable results ($result) of several rows of data or object like this:

PS> $result | ft -auto;
name   value
----   -----
a          1
a          2
b          30
b          20
....

what I need to get all the rows of name and max(value) like this filtered output:

PS> $result | ? |ft -auto
name   value
----   -----
a          2
b          30
....

Not sure what command or filters available (as ? in above) so that I can get each name and only the max value for the name out?

Answer 1

This should do the trick:

PS> $result | Foreach {$ht=@{}} `
                      {if ($_.Value -gt $ht[$_.name].Value) {$ht[$_.Name]=$_}} `
                      {$ht.Values}

This is essentially using the Begin/Process/End scriptblock parameters of the Foreach-Object cmdlet to stash input objects with a max value based on a key into a hashtable.

Note: watch out for extra spaces after the line continuation character (`) - there shouldn't be any.

Answer 2

$result | group name | select name,@{n='value';e={ ($_.group | measure value -max).maximum}}