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 usenumpy.append() andnumpy.concatenate(). This function can help us to append a single value as well as multiple values at the end of the array. In this article, we will also see how to append elements to theNumPyarray.
Appending Values at the End of an NumPy Array
Below are the ways by which we can append values at the end of aNumPyArray inPython:
- Appending a Single Value to a 1D Array
- Appending Another Array at the End of a 1D Array
- Appending Values at the End Using Concatenation
- Appending with a Different Array Type
- Appending Using List Comprehension and
numpy.concatenate - Appending Values at the End of the N-Dimensional Array
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 moduleimportnumpyasnp# 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 moduleimportnumpyasnp# 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 Using Concatenation
In this example, two 2D arrays,arr1 andarr2, are vertically stacked usingnp.concatenate() along the 0th axis, resulting in a combined 2D array.
Python3# importing the moduleimportnumpyasnparr1=np.array([[1,2],[3,4]])arr2=np.array([[5,6]])combined=np.concatenate((arr1,arr2),axis=0)print(combined)
Output:
[[1 2]
[3 4]
[5 6]]
Appending with a Different Array Type
In this example, a 1D integer arrayarr and a 1D float arrayarr_float are appended together usingnp.append(), resulting in an upcasted float array as the output.
Python3# importing the moduleimportnumpyasnparr=np.array([1,2,3])arr_float=np.array([4.0,5.0])combined=np.append(arr,arr_float)print(combined)# Output: [1. 2. 3. 4. 5.]
Output:
[1. 2. 3. 4. 5.]
Appending Using List Comprehension andnumpy.concatenate
In this example, multiple arrays, includingarr and two arrays fromvalues_to_append, are concatenated usinglist comprehension andnp.concatenate(), producing a single combined array.
Python3# importing the moduleimportnumpyasnparr=np.array([1,2,3,4,5])values_to_append=[np.array([6,7]),np.array([8,9])]combined=np.concatenate([arr]+values_to_append)print(combined)
Output:
[1 2 3 4 5 6 7 8 9]
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 moduleimportnumpyasnp# 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]]