Is there a concise emacs lisp equivalent of Python's [n:m] list slices?

Question

One thing I find myself missing in emacs lisp is, surprisingly, a particular bit of list manipulation. I miss Python's concise list slicing.

>>> mylist = ["foo", "bar", "baz", "qux", "frobnitz"] >>> mylist[1:4] ['bar', 'baz', 'qux'] 

I see the functions butlast and nthcdr in the emacs documentation, which would give the same results from code like this:

(setq mylist '("foo" "bar" "baz" "qux" "frobnitz")) (butlast (nthcdr 1 mylist) 1) ;; ("bar" "baz" "qux") 

Is there a more concise way of getting a list slice than combining butlast and nthcdr?

Answer 1

Sure there is:

(require 'cl-lib) (setq mylist '("foo" "bar" "baz" "qux" "frobnitz")) (cl-subseq mylist 1 4) ;; ("bar" "baz" "qux") 

In modern Emacs, please note cl is deprecated see In Emacs, what does this error mean? "Warning: cl package required at runtime"

Answer 2

Common Lisp library is great, but if your codebase becomes large and you want to write concise code in functional style, I endorse dash.el library, which provides enormous amount of functions for list and tree manipulations. There is a function -slice that behaves just like Python's slicing:

(-slice (number-sequence 1 10) 1 7 2) ; (2 4 6) 

Arguments are in order: list, start, (optional) stop, (optional) step.