Hi Marusia,
On Thu, Oct 28, 2010 at 7:02 AM, m.rebolledo
<[email protected]> wrote:
> Hello,
> how to do the union of several lists (more than two)?
Lists are multisets, so I assume you mean to combine several lists
into one, while retaining duplicate elements. You could do so using
the list concatenation operator "+":
sage: L1 = [2, 3, 5, 7, 11]
sage: L2 = ["a", "b", "c", 13]
sage: L3 = [1/2, 1/3, 1/4]
sage: L1 + L2 + L3
[2, 3, 5, 7, 11, 'a', 'b', 'c', 13, 1/2, 1/3, 1/4]
Via the list method extend():
sage: L = []
sage: L.extend(L1)
sage: L.extend(L2)
sage: L.extend(L3)
sage: L
[2, 3, 5, 7, 11, 'a', 'b', 'c', 13, 1/2, 1/3, 1/4]
Or use the Sage built-in function flatten():
sage: flatten([L1, L2, L3])
[2, 3, 5, 7, 11, 'a', 'b', 'c', 13, 1/2, 1/3, 1/4]
If you really want to remove duplicate elements in the final combined
list, use Set():
sage: L1 = [1, 2]
sage: L2 = [2, 3, 4]
sage: L3 = ["a", "b"]
sage: Set(L1 + L2 + L3)
{'a', 1, 2, 3, 4, 'b'}
sage: list(Set(L1 + L2 + L3))
['a', 1, 2, 3, 4, 'b']
> and how to
> remove some elements of the lists?
Use the operator del:
sage: L
[2, 3, 5, 7, 11, 'a', 'b', 'c', 13, 1/2, 1/3, 1/4]
sage: L[0]
2
sage: del L[0]; L
[3, 5, 7, 11, 'a', 'b', 'c', 13, 1/2, 1/3, 1/4]
sage: L[-1]
1/4
sage: del L[-1]; L
[3, 5, 7, 11, 'a', 'b', 'c', 13, 1/2, 1/3]
> I know that it is probably
> elementary but I did not find it in the help... :(
See the Python tutorial [1] for some introductory materials on using
lists. This page [2] and this page [3] provide detailed information on
operations on lists.
[1] http://docs.python.org/tutorial/introduction.html#lists
[2]
http://docs.python.org/library/stdtypes.html#sequence-types-str-unicode-list-tuple-buffer-xrange
[3] http://docs.python.org/library/stdtypes.html#typesseq-mutable
--
Regards
Minh Van Nguyen
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