Append some columns to a list of list matrix

Question

I have some troubles in merging two list of lists to one. I think there is a simple solution, but I’m stuck for hours.

My two list of lists are for example:

a=[['1','2'],['3','4']]
b=[['5','6'],['7','8']]

And what I try to get is:

c=[['1','2','5','6'],['3','4','7','8']]

But I don’t know how many rows and columns the lists have.

I tried to use the zip command but it produced something like:

[(['1','2'],['5','6']),(['3','4'],['7','8'])]

Thanks very much for any help on this issue!!!

Maybe something like How can I add an additional row and column to an array? would work but I suppose there is an simpler solution.

Asked By: Matthias La

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Source

Answer 1

[sum(ai_bi, []) for ai_bi in zip(a, b)]

which scales to n lists of lists :

L = (a, b, ...)
[sum(el, []) for el in zip(*L)]

Answered By: Nicolas Barbey

Answer 2

If your lists have the same lenght:

c = []
for idx in range(len(a)):
    c.append(a[idx]+b[idx])

Not very elegant though.

Answered By: scroll_lock

Answer 3

>>> a=[['1','2'],['3','4']]
>>> b=[['5','6'],['7','8']]
>>> [x + y for x, y in zip(a, b)]
[['1', '2', '5', '6'], ['3', '4', '7', '8']]

Answered By: jamylak

Answer 4

If the two lists are of the same length, you could use a simple loop:

listone = [['1','2'],['3','4']]
listtwo = [['5','6'],['7','8']]
newlist = []

for i in range(0, len(data)):
    newlist.append(listone[i] + listtwo[i])

print(newlist)
[['1','2','5','6'],['3','4','7','8']]

Answered By: Snow

Answer 5

You can also use sympy Matrix object :

Input:

a=[['1','2'],['3','4']]
b=[['5','6'],['7','8']]

import sympy as sp

c = sp.Matrix(a).col_insert(len(a), sp.Matrix(b))
c.tolist()

Output:

[[1, 2, 5, 6], [3, 4, 7, 8]]

Answered By: Erdem Şen

Append some columns to a list of list matrix

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