CODEWITHSUNDEEP
pythontuplesreverse
Benard
Benard

Reputation: 41

python list reverse and merge

I have these two lists

a = [(0,1), (1,2), (3,4)]
b = [[(0,1), (6,7), (8,9)], [(4,5), (7,15), (20,25)], [(18,17), (3,4)]]

what i need is check if the first tuple in a exists in b then merge its reverse so expected output is

ab = [[(3,4),(1,2),(0,1),(6,7), (8,9)], [(4,5), (7,15), (20,25)], [(18,17),(3,4)]]

my sample code is:

import copy
ab = copy.deepcopy(b)

for coord in b:
    if a[0] in coord:
        #print "Yes", coord.index(a[0])
        ab.insert(coord.index(a[0]), a[::-1])

print ab

But it doesn't give me the output i want. Anybody out there who can help? thanks

Upvotes: 2

Views: 526

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1122282

Use a list comprehension to rebuild b:

ab = [a[:0:-1] + sub if a[0] in sub else sub for sub in b]

The a[:0:-1] slice not only reverses a, it also excludes the first element of a to prevent duplicates in the output:

>>> a = [(0,1), (1,2), (3,4)]
>>> b = [[(0,1), (6,7), (8,9)], [(4,5), (7,15), (20,25)], [(18,17), (3,4)]]
>>> [a[:0:-1] + sub if a[0] in sub else sub for sub in b]
[[(3, 4), (1, 2), (0, 1), (6, 7), (8, 9)], [(4, 5), (7, 15), (20, 25)], [(18, 17), (3, 4)]]

Upvotes: 1

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