List Functions

Hi All,

I am just stuck on syntax for some of the list functions.

I use Flatten, Last or First all the time by just using an expression node and something like this:

expression1.Flatten() or expression1.Last() or expression1.First()    where I have an array or List in expression 1.

I would like to use RemoveDuplicates and in the help file it indicates the syntax as object[] RemoveDuplicates(object[] list) similar to Flatten object[] Flatten(object[] list)

However trying the same approach 

expression2.RemoveDuplicates() gives me an error: "unevaluable('You may not modify this object')

Just wondering what I have wrong.

Thanks

Wayne