How do you extract a column from a multi-dimensional array? How do you extract a column from a multi-dimensional array? python python

How do you extract a column from a multi-dimensional array?


>>> import numpy as np>>> A = np.array([[1,2,3,4],[5,6,7,8]])>>> Aarray([[1, 2, 3, 4],    [5, 6, 7, 8]])>>> A[:,2] # returns the third colummarray([3, 7])

See also: "numpy.arange" and "reshape" to allocate memory

Example: (Allocating a array with shaping of matrix (3x4))

nrows = 3ncols = 4my_array = numpy.arange(nrows*ncols, dtype='double')my_array = my_array.reshape(nrows, ncols)


Could it be that you're using a NumPy array? Python has the array module, but that does not support multi-dimensional arrays. Normal Python lists are single-dimensional too.

However, if you have a simple two-dimensional list like this:

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

then you can extract a column like this:

def column(matrix, i):    return [row[i] for row in matrix]

Extracting the second column (index 1):

>>> column(A, 1)[2, 6]

Or alternatively, simply:

>>> [row[1] for row in A][2, 6]


If you have an array like

a = [[1, 2], [2, 3], [3, 4]]

Then you extract the first column like that:

[row[0] for row in a]

So the result looks like this:

[1, 2, 3]


matomo