Subtracting powershell arrays elements and storing the value in a new variable

Question

Have a question on powershell and hopeful will get some hint to get me going in the right direction.

I have a variable which has data stored in it for example $A will output

Year  Cost
----  ----

1997   12
1998   42
1999   6
2000   12
2001   14

I want to add another column here, lets say Trend and compute the difference between the years for example

Year  Cost     Trend

1997   12        0
1998   42       30 (42-12)
1999   6       -36 (6-42) 

Any hints will be really helpful

Answer 1

You could loop through each row comparing it to the previous and then create a new object from the results like so:

$result = 0..($a.count - 1) | % {
    if($_ -eq 0) {$t = $a[$_].Cost} else {$t = $a[$_].Cost - $a[$_ - 1].Cost}
    New-Object PSObject -property @{
    Year = $a[$_].Year
    Cost = $a[$_].Cost
    Trend = $t
    }
 }

$result