Transposing a 2D List in Python

Transposing a 2-dimensional list in Python is especially useful when reading data that’s formatted similar to this:

X   Y   Z
1   2   9
2   5   6
3   6   5
...

Usually, you’ll parse the input line by line and end up with an array that looks something like this:

>>> print(data)
[[1, 2, 9], [2, 5, 6], [3, 6, 5], ...]

This usually isn’t useful though, as we normally want the x, y, and z values grouped together. Doing this is simple with the help of zip() and list unpacking via *. Simply do the following to convert the data into a 2d list:

data = [list(i) for i in zip(*data)]

The result will be:

>>> print(data)
[[1, 2, 3], [2, 5, 6], [9, 6, 5]]

If you do this often, you may want to create a function to do this for you:

def transpose(inputdata):
    return [list(i) for i in zip(*inputdata)]

Then you can simply call transpose(data) and it will return a new list with the data transposed. To overwrite the data variable, simply assign it the value, by calling data = transpose(data)