Let us see how to append values at the end of a NumPy array. Adding values at the end of the array is a necessary task especially when the data is not fixed and is prone to change. For this task we can use numpy.append(). This function can help us to append a single value as well as multiple values at the end of the array.
Syntax : numpy.append(array, values, axis = None)
Appending a single value to a 1D array.
For a 1D array, using the axis argument is not necessary as the array is flattened by default.
python3
# importing the moduleimport numpy as np# creating an arrayarr = np.array([1, 8, 3, 3, 5])print('Original Array : ', arr)# appending to the arrayarr = np.append(arr, [7])print('Array after appending : ', arr) |
Output :
Original Array : [1 8 3 3 5] Array after appending : [1 8 3 3 5 7]
Appending another array at the end of a 1D array
You may pass a list or an array to the append function, the result will be the same.
python3
# importing the moduleimport numpy as np# creating an arrayarr1 = np.array([1, 2, 3])print('First array is : ', arr1)# creating another arrayarr2 = np.array([4, 5, 6])print('Second array is : ', arr2)# appending arr2 to arr1arr = np.append(arr1, arr2)print('Array after appending : ', arr) |
Output :
First array is : [1 2 3] Second array is : [4 5 6] Array after appending : [1 2 3 4 5 6]
Appending values at the end of the n-dimensional array
It is important that the dimensions of both the array matches otherwise it will give an error.
python3
# importing the moduleimport numpy as np# create an arrayarr = np.arange(1, 13).reshape(2, 6)print('Original Array')print(arr, '\n')# create another array which is# to be appended column-wisecol = np.arange(5, 11).reshape(1, 6)print('Array to be appended column wise')print(col)arr_col = np.append(arr, col, axis=0)print('Array after appending the values column wise')print(arr_col, '\n')# create an array which is# to be appended row wiserow = np.array([1, 2]).reshape(2, 1)print('Array to be appended row wise')print(row)arr_row = np.append(arr, row, axis=1)print('Array after appending the values row wise')print(arr_row) |
Output :
Original Array [[ 1 2 3 4 5 6] [ 7 8 9 10 11 12]] Array to be appended column wise [[ 5 6 7 8 9 10]] Array after appending the values column wise [[ 1 2 3 4 5 6] [ 7 8 9 10 11 12] [ 5 6 7 8 9 10]] Array to be appended row wise [[1] [2]] Array after appending the values row wise [[ 1 2 3 4 5 6 1] [ 7 8 9 10 11 12 2]]
