Posts: 39
Threads: 14
Joined: Oct 2018
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List = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
step = 4
def ResetCR (l, stp):
K = []
if stp != 0:
for i in range(1, int(len(l)/stp)+1):
K.append(l[i*stp - 1])
l = [x for x in l if x not in K]
stp = stp - 1
return ResetCR(l,stp)
if stp == 0:
return K
F = ResetCR(List,step)
print (F)
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I'm trying to change the order of a list. If the "K = []" is out side the function, it works. However, I'm wondering is there a way to keep the variable 'K' inside the function?
Posts: 4,220
Threads: 97
Joined: Sep 2016
Is there some reason you need to use recursion?
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def reset2 (l, stp):
k = []
for s in range(stp, 0, -1):
for i in range(1, int(len(l) / s) + 1):
k.append(l[i * s - 1])
l = [x for x in l if x not in k]
return k
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Posts: 39
Threads: 14
Joined: Oct 2018
(Mar-05-2019, 03:34 PM)ichabod801 Wrote: Is there some reason you need to use recursion?
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def reset2 (l, stp):
k = []
for s in range(stp, 0, -1):
for i in range(1, int(len(l) / s) + 1):
k.append(l[i * s - 1])
l = [x for x in l if x not in k]
return k
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Just to practice recursion... Thank you for the solution!
Posts: 4,220
Threads: 97
Joined: Sep 2016
In terms of recursion, my first thought was to have K be a parameter, defaulting to an empty list, and passing the modified K when you recurse. However, there are problems with using empty lists as parameter defaults. You would have to use None as the default, and then replace it with a list in the body of the function (if it is None).
Posts: 39
Threads: 14
Joined: Oct 2018
(Mar-05-2019, 04:11 PM)ichabod801 Wrote: In terms of recursion, my first thought was to have K be a parameter, defaulting to an empty list, and passing the modified K when you recurse. However, there are problems with using empty lists as parameter defaults. You would have to use None as the default, and then replace it with a list in the body of the function (if it is None).
My question is if I replace K in the function with a list and the list is not empty, how does the ".append" effect the list or should I still use ".append" to change the list? Also, in that way, I need a K outside the function.
Posts: 4,220
Threads: 97
Joined: Sep 2016
I'm not sure I understand the question. If you have a K in the function as a non-empty list, append will add to what is already in the list. But if you are defining K in the function, you will have the same problem of it resetting every time you recurse. But if you have a default, and pass the modified list each time you recurse, it doesn't reset.
Posts: 39
Threads: 14
Joined: Oct 2018
(Mar-05-2019, 06:32 PM)ichabod801 Wrote: I'm not sure I understand the question. If you have a K in the function as a non-empty list, append will add to what is already in the list. But if you are defining K in the function, you will have the same problem of it resetting every time you recurse. But if you have a default, and pass the modified list each time you recurse, it doesn't reset.
Thank you! It is very helpful. I think I figured it out.
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List = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
step = 4
def ResetCR (l, stp, K = None):
if K is None:
K = []
if stp != 0:
for i in range(1, int(len(l)/stp)+1):
K.append(l[i*stp - 1])
l = [x for x in l if x not in K]
stp = stp - 1
return ResetCR(l,stp,K)
if stp == 0:
return K
F = ResetCR(List,step)
print (F)
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