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Truncate a List

leto

Hello All,

I have a list with a certain length.

I need to truncate it to make is a shorter list.

Is there a function that can do this most efficiently?

If not, any suggestion on the most efficient way to do this?

Thanks All.

  • DavidJHutchins

    One possible solution would be to use the undocumented 'unique' function...

    testdata = list( "a" "z" "q" "w" "s" "x" "a")

    ("a" "z" "q" "w" "s"

    "x" "a"

    )

    unique(testdata)

    Loading skillExt.cxt

    ("a" "z" "q" "w" "s"

    "x"

    )

  • leto
    in reply to DavidJHutchins

    Thank you David.  What i meant was if I had a list that was 5 elements and I want to create a copy of the same list but only up to 3 elements. Could it be done with a function?

  • DavidJHutchins

    try calling cdr() twice to remove the first 2 entries

    D:\Temp>il_allegro
    > testdata = list( "a" "z" "q" "w" "s")
    ("a" "z" "q" "w" "s")
    > length(testdata)
    5
    > newdata=cdr(cdr(testdata))
    ("q" "w" "s")
    > length(newdata)
    3
    > exit

    D:\Temp>

  • eDave

    nthcdr does this.

    eg. nthcdr(2 '(1 2 3 4)) -> (3 4)

    reverse(nthcdr(2 reverse('(1 2 3 4 5)))) -> (1 2 3)

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