As this question is been 7 years before, in the latest version which I am using is numpy version 1.13, and python3, I am doing the same thing with adding a row to a matrix, remember to put a double bracket to the second argument, otherwise, it will raise dimension error.
In here I am adding on matrix A
1 2 3
4 5 6
with a row
7 8 9
same usage in np.r_
A = [[1, 2, 3], [4, 5, 6]]
np.append[A, [[7, 8, 9]], axis=0]
>> array[[[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]]
#or
np.r_[A,[[7,8,9]]]
Just to someone's intersted, if you would like to add a column,
array = np.c_[A,np.zeros[#A's row size]]
following what we did before on matrix A, adding a column to it
np.c_[A, [2,8]]
>> array[[[1, 2, 3, 2],
[4, 5, 6, 8]]]
If you want to prepend, you can just flip the order of the arguments, i.e.:
np.r_[[[7, 8, 9]], A]
>> array[[[7, 8, 9],
[1, 2, 3],
[4, 5, 6]]]
Given a Numpy array, the task is to add rows/columns basis on requirements to the Numpy array. Let’s see a few examples of this problem in Python.
Add columns in the Numpy array
Method 1: Using np.append[]
Python3
import numpy as np
ini_array = np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
print["initial_array : ", str[ini_array]];
column_to_be_added = np.array[[[1], [2], [3]]]
arr = np.append[ini_array, column_to_be_added, axis=1]
print ["resultant array", str[result]]
Output:
initial_array : [[ 1 2 3] [45 4 7] [ 9 6 10]] resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 2: Using np.concatenate
Python3
import numpy as np
ini_array = np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
column_to_be_added = np.array[[[1], [2], [3]]]
arr =
np.concatenate[[ini_array, column_to_be_added], axis=1]
print ["resultant array", str[result]]
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 3: Using np.insert[]
Python3
import numpy as np
ini_array =
np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
column_to_be_added = np.array[[[1], [2], [3]]]
arr = np.insert[ini_array, 0, column_to_be_added, axis=1]
print ["resultant array", str[result]]
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 4: Using np.hstack[]
Python3
import numpy as np
ini_array = np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
column_to_be_added =
np.array[[1, 2, 3]]
result = np.hstack[[ini_array, np.atleast_2d[column_to_be_added].T]]
print ["resultant array", str[result]]
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 5: Using np.column_stack[]
Python3
import
numpy as np
ini_array = np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
column_to_be_added = np.array[[1, 2, 3]]
result = np.column_stack[[ini_array, column_to_be_added]]
print ["resultant array", str[result]]
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Add row in Numpy array
Method 1: Using np.r_
Python3
import numpy as np
ini_array = np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
print["initial_array : ", str[ini_array]];
row_to_be_added = np.array[[1, 2, 3]]
result = np.r_[ini_array,[row_to_be_added]]
print ["resultant array", str[result]]
Output:
initial_array : [[ 1 2 3] [45 4 7] [ 9 6 10]] resultant array [[ 1 2 3] [45 4 7] [ 9 6 10] [ 1 2 3]]
Method 2: Using np.insert
Python3
import numpy as np
ini_array = np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
row_to_be_added = np.array[[1, 2, 3]]
row_n =
arr.shape[0]
arr = np.insert[ini_array,row_n,[row_to_be_added],axis= 0]
print ["resultant array", str[result]]
Output:
resultant array [[ 1 2 3] [45 4 7] [ 9 6 10] [ 1 2 3]]
Method 3: Using np.vstack[]
Python3
import numpy as np
ini_array =
np.array[[[1, 2, 3], [45, 4, 7], [9, 6, 10]]]
row_to_be_added = np.array[[1, 2, 3]]
result = np.vstack [[ini_array, row_to_be_added] ]
print ["resultant array", str[result]]
Output:
resultant array [[ 1 2 3] [45 4 7] [ 9 6 10] [ 1 2 3]]
Method 4: Using numpy.append[]
Sometimes we have an empty array and we need to append rows in it. Numpy provides the function to append a row to an empty Numpy array using numpy.append[] function.
Example 1: Adding new rows to an empty 2-D array
Python3
import numpy as np
empt_array =
np.empty[[0,2], int]
print["Empty array:"]
print[empt_array]
empt_array = np.append[empt_array, np.array[[[10,20]]], axis=0]
empt_array = np.append[empt_array, np.array[[[40,50]]], axis=0]
print["\nNow array is:"]
print[empt_array]
Empty array: [] Now array is: [[10 20] [40 50]]
Example 2: Adding new rows to an empty 3-D array
Python3
import numpy as np
empt_array = np.empty[[0,3], int]
print["Empty array:"]
print[empt_array]
empt_array = np.append[empt_array, np.array[[[10,20,40]]], axis=0]
empt_array = np.append[empt_array, np.array[[[40,50,55]]], axis=0]
empt_array =
np.append[empt_array, np.array[[[40,50,55]]], axis=0]
print["\nNow array is:"]
print[empt_array]
Empty array: [] Now array is: [[10 20 40] [40 50 55] [40 50 55]]
Example 3: Adding new rows to an empty 4-D array
Python3
import numpy as np
empt_array = np.empty[[0,4], int]
print["Empty array:"]
print[empt_array]
empt_array = np.append[empt_array, np.array[[[100,200,400,888]]], axis=0]
empt_array = np.append[empt_array, np.array[[[405,500,550,558]]], axis=0]
empt_array = np.append[empt_array, np.array[[[404,505,555,145]]], axis=0]
empt_array =
np.append[empt_array, np.array[[[44,55,550,150]]], axis=0]
print["\nNow array is:"]
print[empt_array]
Empty array: [] Now array is: [[100 200 400 888] [405 500 550 558] [404 505 555 145] [ 44 55 550 150]]