[SOLVED] Python: Range or numpy Arange with end limit include

Issue

I am looking to get :

input:

arange(0.0,0.6,0.2)

output:

0.,0.4

I want

0.,0.2,0.4,0.6

how do i achieve using range or arange. If not what is alternate ?

Solution

In short

I wrote a function crange, which does what you require.
In the example below, orange does the job of numpy.arange

crange(1, 1.3, 0.1) >>> [1.  1.1 1.2 1.3]
orange(1, 1.3, 0.1) >>> [1.  1.1 1.2]
crange(0.0, 0.6, 0.2) >>> [0.  0.2 0.4 0.6]
orange(0.0, 0.6, 0.2) >>> [0.  0.2 0.4]

Background information

I had your problem a view times as well. I usually quick-fixed it with adding a small value to stop. As mentioned by Kasrâmvd in the comments, the issue is a bit more complex, as floating point rounding errors can occur in numpy.arange (see here and here).

Unexpected behavior can be found in this example:

>>> numpy.arange(1, 1.3, 0.1)
array([1. , 1.1, 1.2, 1.3])

To clear up things a bit for myself, I decided to stop using numpy.arange if not needed specifically. I instead use my self defined function orange to avoid unexpected behavior. This combines numpy.isclose and numpy.linspace.

Here is the Code

Enough bla bla – here is the code ^^

import numpy as np

def cust_range(*args, rtol=1e-05, atol=1e-08, include=[True, False]):
    """
    Combines numpy.arange and numpy.isclose to mimic
    open, half-open and closed intervals.
    Avoids also floating point rounding errors as with
    >>> numpy.arange(1, 1.3, 0.1)
    array([1. , 1.1, 1.2, 1.3])

    args: [start, ]stop, [step, ]
        as in numpy.arange
    rtol, atol: floats
        floating point tolerance as in numpy.isclose
    include: boolean list-like, length 2
        if start and end point are included
    """
    # process arguments
    if len(args) == 1:
        start = 0
        stop = args[0]
        step = 1
    elif len(args) == 2:
        start, stop = args
        step = 1
    else:
        assert len(args) == 3
        start, stop, step = tuple(args)

    # determine number of segments
    n = (stop-start)/step + 1

    # do rounding for n
    if np.isclose(n, np.round(n), rtol=rtol, atol=atol):
        n = np.round(n)

    # correct for start/end is exluded
    if not include[0]:
        n -= 1
        start += step
    if not include[1]:
        n -= 1
        stop -= step

    return np.linspace(start, stop, int(n))

def crange(*args, **kwargs):
    return cust_range(*args, **kwargs, include=[True, True])

def orange(*args, **kwargs):
    return cust_range(*args, **kwargs, include=[True, False])

print('crange(1, 1.3, 0.1) >>>', crange(1, 1.3, 0.1))
print('orange(1, 1.3, 0.1) >>>', orange(1, 1.3, 0.1))
print('crange(0.0, 0.6, 0.2) >>>', crange(0.0, 0.6, 0.2))
print('orange(0.0, 0.6, 0.2) >>>', orange(0.0, 0.6, 0.2))

Answered By – Markus Dutschke

Answer Checked By – Willingham (BugsFixing Volunteer)

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