Example 1: python how to pad a numpy array with zeros
# Basic syntax:
# For 1D array:
np.pad(numpy_array, (pad_left, pad_right), 'constant')
# For 2D array:
np.pad(numpy_array, ((pad_top, pad_bottom), (pad_left, pad_right)), 'constant')
# Example usage:
import numpy as np
numpy_array = np.array([1,2,3,4,5]) # 1D array
np.pad(numpy_array, (2, 3), 'constant') # Pad 2 left, 3 right
--> array([0, 0, 1, 2, 3, 4, 5, 0, 0, 0])
numpy_array = np.array([[1,2],[3,4]]) # 2D array
array([[1, 2], # Before padding
[3, 4]])
np.pad(numpy_array, ((1,2),(2,1)), 'constant') # Pad 1 top, 2 bottom, 2 left, 1 right
array([[0, 0, 0, 0, 0], # After padding
[0, 0, 1, 2, 0],
[0, 0, 3, 4, 0],
[0, 0, 0, 0, 0],
[0, 0, 0, 0, 0]])
Example 2: np.pad
>>> np.pad(a, [(1, ), (2, )], mode='constant')
array([[ 0., 0., 0., 0., 0., 0., 0., 0., 0.],
[ 0., 0., 1., 1., 1., 1., 1., 0., 0.],
[ 0., 0., 1., 1., 1., 1., 1., 0., 0.],
[ 0., 0., 1., 1., 1., 1., 1., 0., 0.],
[ 0., 0., 0., 0., 0., 0., 0., 0., 0.]])
Example 3: numpy convert 1d array to 2d
import numpy as np
# 1D array
one_dim_arr = np.array([1, 2, 3, 4, 5, 6])
# to convert to 2D array
# we can use the np.ndarray.reshape(shape) function
# here shape is given by two integers seperated by a comma
# the two integers specify m,n for the new matrix
# ensure that the matrix that you are trying to generate
# has a size that meets the number of elements in the 1D array.
# for that make sure that
# m * n = number of elements in the one dimentional array
two_dim_arr = one_dim_arr.reshape(1, 6)
#which returns a 2D array
print(two_dim_arr)
# confirmed by the array.ndim attribute
print(two_dim_arr.ndim)
# you can even specify one of the dimensions as unknown by passing -1
# numpy will infer the length using the array and remaining dimensions
two_dim_arr = one_dim_arr.reshape(1,-1)
Example 4: numpy convert 1d array to 2d
import numpy as np
# 1D array
one_dim_arr = np.array([1, 2, 3, 4, 5, 6])
# To convert to 2D array
# we can use the np.newaxis to increase the dimesions in a array
# Using np.newaxis will increase the dimensions of your array by one dimension when used once.
two_dim_arr = one_dim_arr[np.newaxis, :]
print(two_dim_arr)
# inserting a axis at the first index creates a row vector
print()
# for column vector, insert axis at the second index
two_dim_arr = one_dim_arr[:,np.newaxis]
print(two_dim_arr)
print()
# we can also expand an array by inserting a new axis at a specified position with np.expand_dims.
two_dim_arr = np.expand_dims(one_dim_arr,axis = 0)
print(two_dim_arr)
print()
two_dim_arr = np.expand_dims(one_dim_arr,axis = 1)
print(two_dim_arr)