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In this chapter, we will discuss about NumPy Array Creation Routines. A new ndarray object can be constructed by any of the following array creation routines or using a low-level ndarray constructor.

NumPy Array Creation Routines numpy.empty

It creates an uninitialized array of specified shapes and dtype. It uses the following constructor −

numpy.empty(shape, dtype = float, order = 'C')

The constructor takes the following parameters.

Sr.No.	Parameter & Description
1	shape shape of an empty array in int or tuple of int
2	DtypeDesired output data type. Optional
3	Order‘C’ for C-style row-major array, ‘F’ for FORTRAN style column-major array

Example

The following code shows an example of an empty array.

import numpy as np 
x = np.empty([3,2], dtype = int) 
print x

The output is as follows −

[[22649312    1701344351] 
 [1818321759  1885959276] 
 [16779776    156368896]]

Note − The elements in an array show random values as they are not initialized.

numpy.zeros

Returns a new array of specified size, filled with zeros.

numpy.zeros(shape, dtype = float, order = 'C')

The constructor takes the following parameters.

Sr.No.	Parameter & Description
1	shape shape of an empty array in int or sequence of int
2	DtypeDesired output data type. Optional
3	Order‘C’ for C-style row-major array, ‘F’ for FORTRAN style column-major array

Example 1

# array of five zeros. Default dtype is float 
import numpy as np 
x = np.zeros(5) 
print x

The output is as follows −

[ 0.  0.  0.  0.  0.]

Example 2

import numpy as np 
x = np.zeros((5,), dtype = np.int) 
print x

Now, the output would be as follows −

[0  0  0  0  0]

Example 3

# custom type 
import numpy as np 
x = np.zeros((2,2), dtype = [('x', 'i4'), ('y', 'i4')])  
print x

It should produce the following output −

[[(0,0)(0,0)]
 [(0,0)(0,0)]]         

numpy.ones

Returns a new array of specified size and type, filled with ones.

numpy.ones(shape, dtype = None, order = 'C')

The constructor takes the following parameters.

Sr.No.	Parameter & Description
1	shape shape of an empty array in int or tuple of int
2	DtypeDesired output data type. Optional
3	Order‘C’ for C-style row-major array, ‘F’ for FORTRAN style column-major array

Example 1

# array of five ones. Default dtype is float 
import numpy as np 
x = np.ones(5) 
print x

The output is as follows −

[ 1.  1.  1.  1.  1.]

Example 2

import numpy as np 
x = np.ones([2,2], dtype = int) 
print x

Now, the output would be as follows −

[[1  1] 
 [1  1]]