CODEWITHSUNDEEP
pythonarraysnumpy
Claudiu S
Claudiu S

Reputation: 1627

NumPy append to 1-column vector

I am trying to cluster pixels using k-means in an image (480 x 640), and so I am trying to initialise an empty numpy array, which represents a 1-column vector.

What I am trying to achieve is get all pixel values from the 2D array and add them in a 1D vertical vector, like this:

[ [ value ],
  [ value ],
  ...
  [ value ] ]

Upvotes: 0

Views: 350

Answers (2)

dawg
dawg

Reputation: 103834

Suppose you have a matrix 640 x 480:

>>> a=np.arange(640*480).reshape(640,480)
>>> a
array([[     0,      1,      2, ...,    477,    478,    479],
       [   480,    481,    482, ...,    957,    958,    959],
       [   960,    961,    962, ...,   1437,   1438,   1439],
       ..., 
       [305760, 305761, 305762, ..., 306237, 306238, 306239],
       [306240, 306241, 306242, ..., 306717, 306718, 306719],
       [306720, 306721, 306722, ..., 307197, 307198, 307199]])

You can assign a columnar value like so:

>>> a[:,479]=0
>>> a
array([[     0,      1,      2, ...,    477,    478,      0],
       [   480,    481,    482, ...,    957,    958,      0],
       [   960,    961,    962, ...,   1437,   1438,      0],
       ..., 
       [305760, 305761, 305762, ..., 306237, 306238,      0],
       [306240, 306241, 306242, ..., 306717, 306718,      0],
       [306720, 306721, 306722, ..., 307197, 307198,      0]])
#                                                         ^^^ Note the 0 here

You can get the columnar value like so:

>>> a[:,478]
array([   478,    958,   1438,   1918, ..., 306238, 306718, 307198])

Upvotes: 1

user3306215
user3306215

Reputation: 36

Is numpy.reshape() what you want?

a = np.array([[1,2,3], [4,5,6]])
a.reshape(6,1)
array([[1],
       [2],
       [3],
       [4],
       [5],
       [6]])

Upvotes: 2

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