Sorting by item_in_another_list
Cameron Walsh
cameron.walsh at gmail.com
Tue Oct 24 06:12:16 CEST 2006
Hi,
I have two lists, A and B, such that B is a subset of A.
I wish to sort A such that the elements in B are at the beginning of A,
and keep the existing order otherwise, i.e. stable sort. The order of
elements in B will always be correct.
for example:
A = [0,1,2,3,4,5,6,7,8,9,10]
B = [2,3,7,8]
desired_result = [2,3,7,8,0,1,4,5,6,9,10]
At the moment I have defined a comparator function:
def sort_by_in_list(x,y):
ret = 0
if x in B:
ret -= 1
if y in B:
ret += 1
return ret
and am using:
A.sort(sort_by_in_list)
which does produce the desired results.
I do now have a few questions:
1.) Is this the most efficient method for up to around 500 elements?
If not, what would be better?
2.) This current version does not allow me to choose a different list
for B. Is there a bind_third function of some description that I could
use to define a new function with 3 parameters, feed it the third (the
list to sort by), and have the A.sort(sort_by_in_list) provide the other
2 variables?
Regards to all,
Cameron.
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