NumPy - Array from Numerical Ranges

The NumPy package contains a number of functions which can be used to create an array from a given numerical range. Below is the list of most commonly used functions for this purpose:

Function	Description
arange()	Return evenly spaced values within a given interval.
linspace()	Returns evenly spaced numbers over a specified interval.
logspace()	Return numbers spaced evenly on a log scale.

Lets discuss these functions in detail:

numpy.arange() function

The numpy.arange() function returns evenly spaced values within a given interval. The values are generated in the range [start, stop) with specified step size.

Syntax

numpy.arange(start, stop, step, dtype=None)

Parameters

`start`	`Optional.` Specify start of the interval (inclusive). The default value is 0.
`stop`	`Required.` Specify end of the interval (exclusive).
`step`	`Optional.` Specify the step size. The default value is 1.
`dtype`	`Optional.` Specify the type of the output array. If dtype is not given, infer the data type from the other input arguments.

Example:

The example below shows how to use arange() function to create arrays.

import numpy as np

#creating array using range [10,55) 
#and step size = 5
Arr1 = np.arange(10,55,5)
print("Arr1 is:", Arr1)

#creating array using range [10,16) 
#and step size = 1 and dtype=float
Arr2 = np.arange(10,16,dtype=float)
print("Arr2 is:", Arr2)

#reshaping the Arr2
Arr3 = Arr2.reshape(2,3)
print("Arr3 is:\n", Arr3)

The output of the above code will be:

Arr1 is: [10 15 20 25 30 35 40 45 50]
Arr2 is: [10. 11. 12. 13. 14. 15.]
Arr3 is:
[[10. 11. 12.]
 [13. 14. 15.]]

numpy.linspace() function

The numpy.linspace() function returns evenly spaced values over a specified interval. The values are generated in the range [start, stop] with specified number of samples. The endpoint of the interval can optionally be excluded.

Syntax

numpy.linspace(start, stop, num=50, endpoint=True, retstep=False, dtype=None)

Parameters

`start`	`Required.` Specify the starting value of the sequence.
`stop`	`Required.` Specify the end value of the sequence, unless endpoint is False. In that case, the sequence consists of all but the last of num + 1 evenly spaced samples, so that stop is excluded. Note that the step size changes when endpoint is False.
`num`	`Optional.` Specify the number of samples to generate. Default is 50. Must be non-negative.
`endpoint`	`Optional.` Specify boolean value. If True, stop is the last sample. Otherwise, it is not included. Default is True.
`retstep`	`Optional.` Specify boolean value. If True, return (samples, step), where step is the spacing between samples.
`dtype`	`Optional.` Specify type of the output array. If dtype is not given, infer the data type from the other input arguments.

Example:

In the example below, linspace() function is used with different parameters to create arrays.

import numpy as np

#creating 5 samples points in the given range
Arr1 = np.linspace(1,5,num=5)
print("Arr1 is:", Arr1)

#when endpoint=False, (num+1) samples are  
#generated and returns samples without last
Arr2 = np.linspace(1,5,num=5,endpoint=False)
print("Arr2 is:", Arr2)

#when retstep=True, returns (samples, step)
Arr3 = np.linspace(1,5,num=5,retstep=True)
print("Arr3 is:", Arr3)

The output of the above code will be:

Arr1 is: [1. 2. 3. 4. 5.]
Arr2 is: [1.  1.8 2.6 3.4 4.2]
Arr3 is: (array([1., 2., 3., 4., 5.]), 1.0)

numpy.logspace() function

The numpy.logspace() function returns numbers spaced evenly on a log scale. The values are generated in the range [base ** start, base ** stop] with specified number of samples. The endpoint of the interval can optionally be excluded.

Syntax

numpy.logspace(start, stop, num=50, endpoint=True, base=10.0, dtype=None)

Parameters

`start`	`Required.` Specify the starting value of the sequence. The starting value is base ** start.
`stop`	`Required.` Specify the end value of the sequence (end value is base ** end), unless endpoint is False. In that case, num + 1 values are spaced over the interval in log-space, of which all but the last (a sequence of length num) are returned.
`num`	`Optional.` Specify the number of samples to generate. Default is 50. Must be non-negative.
`endpoint`	`Optional.` Specify boolean value. If True, stop is the last sample. Otherwise, it is not included. Default is True.
`base`	`Optional.` Specify base of the log space. The step size between the elements in ln(samples) / ln(base) (or log_base(samples)) is uniform. Default is 10.0.
`dtype`	`Optional.` Specify type of the output array. If dtype is not given, infer the data type from the other input arguments.

Example:

In the example below, logspace() function is used with different parameters to create arrays.

import numpy as np

#creating 5 samples points in the given range
Arr1 = np.logspace(1,2,num=5)
print("Arr1 is:", Arr1)

#when endpoint=False, (num+1) samples are  
#generated and returns samples without last 
Arr2 = np.logspace(1,2,num=5,endpoint=False)
print("Arr2 is:", Arr2)

#using base=2.0
Arr3 = np.logspace(1,2,num=5,base=2.0)
print("Arr3 is:", Arr3)

The output of the above code will be:

Arr1 is: [10.     17.7827941   31.6227766   56.23413252  100.       ]
Arr2 is: [10.     15.84893192  25.11886432  39.81071706  63.09573445]
Arr3 is: [2.      2.37841423   2.82842712   3.36358566   4.         ]