Suppose I have several lists of length n:
a = [1, 2, 3]
b = [4, 5, 6]
c = [7, 8, 9]
d = [-1, -2, -3]
I put those lists into a list:
x = [a, b, c]
Now I'd like to end up with the following list:
y = [[1, 4, 7, -1], [2, 5, 8, -2], [3, 6, 9, -3]]
What is a quick and pythonic way to do so? (To get from x to y.)
The entries could be anything, I use numbers just because they visualize good.
There is a very simple and pythonic way to "reverse-zip" a list in this way. Simple use the zip function and the unpacking operator *:
>>> y = zip(*x)
>>> list(y)
[(1, 4, 7, -1), (2, 5, 8, -2), (3, 6, 9, -3)]
For more information about what is going on, see What is the inverse function of zip in python?
If it is important that it be a list of lists, instead of a list of tuples, you can do the following:
>>> [list(i) for i in zip(*x)]
[[1, 4, 7, -1], [2, 5, 8, -2], [3, 6, 9, -3]]
You can do it in one line of code:
[[z[i] for z in x] for i in range(len(x[0]))]
What it does is that to iterate over all indexes (i) and then iterate over all lists in x (z) and create a new list.
You can try zip
>>> result = zip(a,b,c,d) # This gives ans as list of tuples [(1, 4, 7, -1), (2, 5, 8, -2), (3, 6, 9, -3)]
>>> result_list = [list(elem) for elem in result] #convert list of tuples to list of list
>>> result_list
[[1, 4, 7, -1], [2, 5, 8, -2], [3, 6, 9, -3]]
