An example of a transformation of a two dimensional array in python

This article illustrates the transformation method of two-dimensional array in python. Share with you for your reference. Specific methods are as follows:

First look at the following code:

arr = [ [1, 2, 3], [4, 5, 6], [7, 8,9], [10, 11, 12]] 
 
print map(list, zip(*arr)) 
print '_-------------------------------------------------' 
print [[r[col] for r in arr] for col in range(len(arr[0]))] 

The operation results are as follows:

[[1, 4, 7, 10], [2, 5, 8, 11], [3, 6, 9, 12]]
_-------------------------------------------------
[[1, 4, 7, 10], [2, 5, 8, 11], [3, 6, 9, 12]]

Here's why:

1. The first method : the map (list, zip (* arr))
Zip ([iterable,... )
This function returns a list of tuples, where thei-th tuple contains thei-th element from each of the argument sequences or iterables.
Zip ()

This function returns a list of tuples where the ith tuple contains the ith element of each argument's element from the queue passed in the argument

Here's another example:

>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> zipped = zip(x, y)
>>> zipped
[(1, 4), (2, 5), (3, 6)]

Zip (*arr) actually returns [(1, 4, 7, 10), (2, 5, 8, 11), (3, 6, 9, 12)], except that each of its elements is a tuple

The map (func, a list) :

The func method is called for each element in the list, returning the list
Parameter *arr is python's syntax for passing arbitrary location-based parameters

2. The second method: [[r[col] for r in arr] for col in range(len(arr[0]))]
The inner derivation changes the elements selected (from the row), and the outer derivation affects the selectors (that is, the columns)

I hope this article has helped you with your Python programming.