numpy rows and columns code example

Example 1: extract column numpy array python

# Extract/ Slice only the 3rd column from the numpy array
print(a2[:,[2]])

Example 2: get column or row of matrix array numpy python

test = numpy.array([[1, 2], [3, 4], [5, 6]])
column = test[:,0]
# column == array([1, 3, 5])
row = test[1,:]
# row == array([3, 4])

Example 3: how to get the first few lines of an ndarray

In [11]: a[:,:2]
Out[11]: 
array([[-0.57098887, -0.4274751 ],
       [-0.22279713, -0.51723555],
       [ 0.67492385, -0.69294472],
       [ 0.41086611,  0.26374238]])

Example 4: data[:,:2]

X = dataset[:,0:3] is interpreted as "All rows for columns 0 through 3" and y = dataset[:,4] is interpreted as "all rows for column 4".