I have two lists:
a = [(1,2,3),(4,5,6)]
b = [7,8]
I want to merge it into:
c = [(1,2,3,7),(4,5,6,8)]
I used zip(a,b) but the result does not seem correct. Can anyone help?
7 Answers
zip() will just pair up the tuples and the integers. You also need to concatenate the tuple and the new item:
c = [aa + (bb,)
for aa, bb in zip(a, b)]
1 Comment
DSM
ISTM this is the most Pythonic solution (and I hope I'm not just saying that because it's how I would do it). No cleverness and no map/lambda combinations, it just does it.
>>> a = [(1,2,3),(4,5,6)]
>>> b = [7,8]
>>> c = zip(*a)+[b] #c looks like [(1,4),(2,5),(3,6),(7,8)]
>>> print zip(*c) #zip it back together
[(1, 2, 3, 7), (4, 5, 6, 8)]
>>>
3 Comments
st0le
This is clever, but I don't find this intuitive. It took a second look. Upvoted never the less.
Joran Beasley
I added some comments to help
Joran Beasley
meh its pretty readable for me... not as much as the map solutions but about equal to the others and more so than some
Try
map ( lambda x: x[0]+(x[1],), zip(a,b))
1 Comment
Joran Beasley
better and shorter than mine ... may want to provide comments in the code though as you might forget what this is doing later
And yet another version:
from itertools import izip
[x+(y,) for x,y in izip(a,b)]
Should be efficient and it expresses what you are really doing in a readable way.
Comments
And yet another:
map(lambda t, e: t + (e,), a, b)
No need to zip and unpack; map can take both lists at once.
3 Comments
Joran Beasley
this is my favorite answer... I didnt know (didnt ever really think about it) you could pass more than 1 list to map... now I do
st0le
@JoranBeasley, This will not work if the
len(a) != len(b). map fills the excess with None and it'll blow up.
tobias_k
@st0le Thanks for pointing this out! But won't an exception be better than silently dropping elements using
zip?print((a[0]+(b[0],),a[1]+(b[1],)))
Comments
This seems clear to me:
[x + (b[i],) for i,x in enumerate(a)]
ais a list of tuples. tuple is an immutable sequence type.