Pivot an array of array? - powershell

Question

The following code defined a matrix.
$a = #('a','b','x',10),
#('a','b','y',20),
#('c','e','x',50),
#('c','e','y',30)
$a | % { "[$_]"}
I want to pivot the array by x and y. The expected result array should be
[a b 10 20]
[c e 50 30]
- - -- --
x y
I think it needs group-object and then mapping. How to use group-object on an array?
(BTW, why the question has been down voted twice?)

Answer 1

You can't use Group-Object with an array (at least not the way you want) since Group-Object works on object properties. A workaround is to organize your rows into a label that you want to group on, followed by the values to assign to the group. Then you can group on the label:
$a | %{
new-object PsObject -prop #{"label" = "$($_[0]),$($_[1])"; value=#{ $_[2]=$_[3]}}
} | Group-Object label
So, then you have a group with your entries stroed as an array of hashtables within each group:
Count Name Group
----- ---- -----
2 a,b {#{value=System.Collections.Hashtable; label=a,b}, #{value=System.Collections.Hashtable; label=a,b}}
2 c,e {#{value=System.Collections.Hashtable; label=c,e}, #{value=System.Collections.Hashtable; label=c,e}}
You can then expand out each row to get the info you desire:
$a | %{
new-object PsObject -prop #{"label" = "$($_[0]),$($_[1])"; value=#{ $_[2]=$_[3]}}
} |
group label | % {
"[$(#($_.Name -split ",") + #($_.Group.value.values))]"
}
which gives:
[a b 10 20]
[c e 50 30]
To answer your second comment, no the above won;t guarantee the order. To guarantee it, you'll have to be explicit:
$a | %{
new-object PsObject -prop #{"label" = "$($_[0]),$($_[1])"; value=#{ $_[2]=$_[3]}}
} |
group label | % {
"[$(#($_.Name -split ",") + #($_.Group.value.x, $_.Group.value.y))]"
}