Here we will learn how to convert 1D NumPy to 2D NumPy Using two methods. Numpy is a Python package that consists of multidimensional array objects and a collection of operations or routines to perform various operations on the array and processing of the array.
Convert a 1D array to a 2D Numpy array using reshape
This package consists of a function called numpy.reshape which is used to convert a 1-D array into a 2-D array of required dimensions (n x m). This function gives a new required shape without changing the data of the 1-D array.
Examples 1:
Convert a 1-D array into a 2-D array of required dimensions (n x m).
Python3
import numpy as np# 1-D array having elements [1 2 3 4 5 6 7 8]arr = np.array([1, 2, 3, 4, 5, 6, 7, 8])# Now we can convert this 1-D array into 2-D in two ways# 1. having dimension 4 x 2arr1 = arr.reshape(4, 2)print ('After reshaping having dimension 4x2:')print (arr1)print ('\n')# 2. having dimension 2 x 4arr2 = arr.reshape(2, 4)print ('After reshaping having dimension 2x4:')print (arr2)print ('\n') |
Output:
After reshaping having dimension 4x2: [[1 2] [3 4] [5 6] [7 8]] After reshaping having dimension 2x4: [[1 2 3 4] [5 6 7 8]]
Example 2:
Let us see an important observation whether we can reshape a 1-D array into any 2-D array.
Python3
import numpy as np# 1-D array having elements [1 2 3 4 5 6 7 8]arr = np.array([1, 2, 3, 4, 5, 6, 7, 8])# Print the 1-D arrayprint('Before reshaping:')print(arr)print('\n')# let us try to convert into 2-D array having dimension 3x3arr1 = arr.reshape(3, 3)print('After reshaping having dimension 3x3:')print(arr1)print('\n') |
Output:
This concludes that the number of elements should be equal to the product of dimension i.e. 3×3=9 but total elements = 8;
Example 3:
Another example is that we can use the reshape method without specifying the exact number for one of the dimensions. Just pass -1 as the value and NumPy will calculate the number.
Python3
import numpy as np# 1-D array having elements [1 2 3 4 5 6 7 8]arr = np.array([1, 2, 3, 4, 5, 6, 7, 8])# Print the 1-D arrayprint('Before reshaping:')print(arr)print('\n')arr1 = arr.reshape(2, 2, -1)print('After reshaping:')print(arr1)print('\n') |
Output:
Before reshaping: [1 2 3 4 5 6 7 8] After reshaping: [[[1 2] [3 4]] [[5 6] [7 8]]]
Convert a 1D array to a 2D Numpy array using numpy.reshape
Here, we are using np.reshape to convert a 1D array to 2 D array. You can divide the number of elements in your array by ncols.
Python3
import numpy as nparr = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12])# np.reshape(A,(-1,ncols))B = np.reshape(arr, (-1, 2))print('2D Numpy array: \n', B) |
Output:
2D Numpy array: [[ 1 2] [ 3 4] [ 5 6] [ 7 8] [ 9 10]
