How to concatenate element-wise two lists in Python?

Question

I have two lists and I want to concatenate them element-wise. One of the list is subjected to string-formatting before concatenation.

For example :

Answer 1

Than can be done elegantly with map and zip:

map(lambda (x,y): x+y, zip(list1, list2))

Example:

In [1]: map(lambda (x,y): x+y, zip([1,2,3,4],[4,5,6,7]))
Out[1]: [5, 7, 9, 11]

Answer 2

inputs:

a = [0, 1, 5, 6, 10, 11] 
b = ['asp1', 'asp1', 'asp1', 'asp1', 'asp2', 'asp2']

concat_func = lambda x,y: x + "" + str(y)

list(map(concat_func,b,a)) # list the map function

output:

['asp10', 'asp11', 'asp15', 'asp16', 'asp210', 'asp211']

Answer 3

If you wanted to concatenate arbitrary number of lists, you could do this:

In [1]: lists = [["a", "b", "c"], ["m", "n", "o"], ["p", "q", "r"]] # Or more

In [2]: lists
Out[2]: [['a', 'b', 'c'], ['m', 'n', 'o'], ['p', 'q', 'r']]    

In [4]: list(map("".join, zip(*lists)))
Out[4]: ['amp', 'bnq', 'cor']

Answer 4

Use zip:

>>> ["{}{:02}".format(b_, a_) for a_, b_ in zip(a, b)]
['asp100', 'asp101', 'asp105', 'asp106', 'asp210', 'asp211']

Answer 5

not using zip. I dunno, I think this is the obvious way to do it. Maybe I just learnt C first :)

c=[]
for i in xrange(len(a)):
    c.append("%s%02d" % (b[i],a[i]))

Answer 6

Other solution (preferring printf formating style over .format() usage), it's also smaller:

>>> ["%s%02d" % t for t in zip(b, a)]
['asp100', 'asp101', 'asp105', 'asp106', 'asp210', 'asp211']