pytutorial/numpy/numerical_ranges​

Making a matrix from numerical ranges

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The goal

Making a matrix from numerical ranges...

Questions to David Rotermund

numpy.arange

numpy.arange([start, ]stop, [step, ]dtype=None, *, like=None)

Return evenly spaced values within a given interval.

arange can be called with a varying number of positional arguments:

arange(stop) : Values are generated within the half-open interval [0, stop) (in other words, the interval including start but excluding stop).

arange(start, stop) : Values are generated within the half-open interval [start, stop).

arange(start, stop, step) Values are generated within the half-open interval [start, stop), with spacing between values given by step.

For integer arguments the function is roughly equivalent to the Python built-in range, but returns an ndarray rather than a range instance.

When using a non-integer step, such as 0.1, it is often better to use numpy.linspace.

Examples:

import numpy as np

print(np.arange(5)) # -> [0 1 2 3 4]
print(np.arange(0, 5)) # -> [0 1 2 3 4]
print(np.arange(2, 5)) # -> [2 3 4]
print(np.arange(0, 5, 2)) # -> [0 2 4]

It can be nicely combined with reshape():

import numpy as np
print(np.arange(0, 9).reshape(3, 3))

Output:

[[0 1 2]
 [3 4 5]
 [6 7 8]]

Do not use it with non-integer values for step!!! This can happen and you don't want this to happen:

import numpy as np

print(np.arange(-3, 0, 0.5, dtype=int)) # -> [-3 -2 -1  0  1  2]