[Tutor] Rearranging a list
Steven D'Aprano
steve at pearwood.info
Thu Feb 26 13:40:20 CET 2015
On Thu, Feb 26, 2015 at 07:13:57AM -0500, Ken G. wrote:
> Assuming I have the following list and code how do I best be able
> rearrange the list as stated below:
>
> list = [0, 0, 21, 35, 19, 42]
Be aware that you have "shadowed" the built-in list function, which
could cause trouble for you.
py> list = [1, 2, 3]
py> # much later, after you have forgotten you shadowed list...
py> characters = list("Hello world")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'list' object is not callable
Oops.
Save yourself future hassles, and pick a name like "L" (don't use "l",
since that looks too similar to digit 1) or "mylist" or "seq" (short for
sequence).
> Using print list[2:6] resulted in the following:
>
> 2 21
> 3 35
> 4 19
> 5 42
I'm pretty sure it doesn't.
py> lst = [0, 0, 21, 35, 19, 42]
py> print(lst[2:6])
[21, 35, 19, 42]
You're obviously doing a lot more than just `print lst[2:6]` to get the
output you say you are getting.
> I would like to rearrange the list as follow:
>
> 5 42
> 3 35
> 2 21
> 4 19
I don't understand how to generalise that. If you know you want that
EXACT output, you can say:
print "5 42"
print "3 35"
etc. to get it. Obviously that's not what you want, but I don't
understand what rule you used to get "5 42" first, "3 35" second,
etc. Where does the 5, 3, 2, 4 come from? What's the rule for getting 42
first, 19 last?
> I tried using list.reverse() and print list[0,6] and it resulted in:
>
> [42, 19, 35, 21, 0, 0] or as printed:
>
> 0 42
> 1 19
> 2 35
> 3 21
> 4 0
> 5 0
>
> In another words, I would desire to show that:
>
> 5 appears 42 times
> 3 appears 35 times
> 2 appears 21 times
> 4 appears 19 times
Huh? Now I'm *completely* confused. Your list was:
[0, 0, 21, 35, 19, 42]
5, 3, 2 and 4 don't appear *at all*. You have:
0 appears twice
21 appears once
35 appears once
19 appears once
42 appears once
> but then I lose my original index of the numbers by reversing. How do I
> best keep the original index number to the rearrange numbers within a list?
No clue what you mean.
--
Steve
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