CODEWITHSUNDEEP
pythonarraysnumpy3d
Oh_canada
Oh_canada

Reputation: 95

How do you create a 3D array (data cube) in python?

I'd like to know how to make a simple data cube (matrix) with three 1D arrays or if there's a simpler way. I want to be able to call a specific value at the end from the cube such as cube[0,2,6].

x = arange(10)
y = arange(10,20,1)
z = arange(20,30,1)

cube = meshgrid(x,y,z)

But this doesn't give the desired result, as it gives mulitple arrays and can't call a specific number easily. I'd like to be able to use this for large data sets that would be laborious to do by hand, later on. Thanks

Upvotes: 1

Views: 6060

Answers (1)

Paul Panzer
Paul Panzer

Reputation: 53029

meshgrid as its name suggests creates an orthogonal mesh. If you call it with 3 arguments it will be a 3d mesh. Now the mesh is 3d arrangement of points but each point has 3 coordinates. Therefore meshgrid returns 3 arrays one for each coordinate.

The standard way of getting one 3d array out of that is to apply a vectorised function with three arguments. Here is a simple example:

>>> x = arange(7)
>>> y = arange(0,30,10)
>>> z = arange(0,200,100)
>>> ym, zm, xm = meshgrid(y, z, x)
>>> xm
array([[[0, 1, 2, 3, 4, 5, 6],
        [0, 1, 2, 3, 4, 5, 6],
        [0, 1, 2, 3, 4, 5, 6]],

       [[0, 1, 2, 3, 4, 5, 6],
        [0, 1, 2, 3, 4, 5, 6],
        [0, 1, 2, 3, 4, 5, 6]]])
>>> ym
array([[[ 0,  0,  0,  0,  0,  0,  0],
        [10, 10, 10, 10, 10, 10, 10],
        [20, 20, 20, 20, 20, 20, 20]],

       [[ 0,  0,  0,  0,  0,  0,  0],
        [10, 10, 10, 10, 10, 10, 10],
        [20, 20, 20, 20, 20, 20, 20]]])
>>> zm
array([[[  0,   0,   0,   0,   0,   0,   0],
        [  0,   0,   0,   0,   0,   0,   0],
        [  0,   0,   0,   0,   0,   0,   0]],

       [[100, 100, 100, 100, 100, 100, 100],
        [100, 100, 100, 100, 100, 100, 100],
        [100, 100, 100, 100, 100, 100, 100]]])
>>> cube = xm + ym + zm
>>> cube
array([[[  0,   1,   2,   3,   4,   5,   6],
        [ 10,  11,  12,  13,  14,  15,  16],
        [ 20,  21,  22,  23,  24,  25,  26]],

       [[100, 101, 102, 103, 104, 105, 106],
        [110, 111, 112, 113, 114, 115, 116],
        [120, 121, 122, 123, 124, 125, 126]]])
>>> cube[0, 2, 6]
26

Upvotes: 2

Related Questions