How to extract a range from a collection in powershell?

Question

I have a large set of items and I want to extract items from it. I need to skip some items from start and some from end.

The following example is simplified.

I first tried to extract the bounding elements:

> ("a", "b", "c", "d", "e")[1,-2]
b
d  

This works as expected.

However when I tried to extract whole range it returns something else than I want (in contrast with Python's ['a', 'b', 'c', 'd', 'e'][1:-1] which works well).

> ("a", "b", "c", "d", "e")[1..-2]
b
a
e
d  

It loops the other way round. How to change the direction of the loop?

I want to get: b c d.

Is there a solution without using the real length of the collection?

Answer 1

1..-2 will not count from the first item until two items from the end. Save the array to a variable and specify the upper bound by calculating the array length minus the items from the end.

$a = "a", "b", "c", "d", "e"
$a[1..($a.length-2)]

Answer 2

Since the range operator does not do what you require, a simple pipeline can accomplish the task at hand, though this will likely impact performance for a large collection.

Start with a collection and the number of elements to trim from top and from bottom:

$a = "a", "b", "c", "d", "e"
($fromTop,$fromBottom) = 1, 2

Use this...

$a | select -skip $fromTop | select -skip $fromBottom -last 1000000

...or, if you have PSCX installed, this more concise and elegant sequence:

$a | skip -first $fromTop -last $fromBottom

Both of those return b c without explicitly using the length property. Adjust the two parameters to tailor the output to different ranges.

Answer 3

To just remov the first two ones you can do that :

$null,$null,$a = "a", "b", "c", "d", "e"