1.

How do you concatenate 2 NumPy arrays?

Answer»

Concatenating 2 arrays by adding elements to the end can be achieved by making use of the concatenate() method of the NumPy package. Syntax:

np.concatenate((a1, a2, ...), axis=0, out=None)

where,


  • a1,a2: arrays of the same shape

  • axis: Represents the axis along which the arrays are joined. The default value is 0.

  • out: If mentioned, it specifies the destination for placing the result.

For example:

import numpy as np
a = np.array([[1, 2], [3, 4]])
b = np.array([[5, 6]])

# Concatenate with axis 0
c = np.concatenate((a,b), axis=0)
print("With axis 0: \n",c )

# Concatenate with axis 1 (b.T represents transpose matrix)
d = np.concatenate((a,b.T), axis=1)
print("With axis 1: \n",d )

The output would be:

With axis 0:
[[1 2]
[3 4]
[5 6]]
With axis 1:
[[1 2 5]
[3 4 6]]

Notice how the arrays are concatenated with different values of the axis.


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