Working of np.arrage() function i n a code

I have looked into the numpy.arrange() documentation, but couldn’t understand how the following command is working:
plt.xticks(numpy.arange(130000)[::20000][2:],[‘11AM day 1’,‘5:30PM day 1’,‘10PM day 1’, ‘3:30AM day 2’, ‘9AM day 2’],rotation=90)

Just for reference, it is part of the following snippet I am working on:
if plot==True:
fig,ax = plt.subplots(figsize=(6,5))
ax.plot(tt, yy, “-k”, linewidth=1, alpha=0.3)
ax.plot(tt, fitfunc(tt), “r-”, label=“Circadian Rhythm”, linewidth=2)
plt.xticks(numpy.arange(130000)[::20000][2:],[‘11AM day 1’,‘5:30PM day 1’,‘10PM day 1’, ‘3:30AM day 2’, ‘9AM day 2’],rotation=90)
plt.legend()
fig.tight_layout()
plt.show()

Hi Afaq,

You asked about the use of numpy.arange in this line of code:

plt.xticks(numpy.arange(130000)[::20000][2:],['11AM day 1','5:30PM day 1','10PM day 1', '3:30AM day 2', '9AM day 2'],rotation=90)

Does this help?

>>> import numpy
>>> numpy.arange(130000)[::20000][2:]
array([ 40000,  60000,  80000, 100000, 120000])

Quite frankly, I think that’s a silly use of numpy. Given that the axis
labels are hard-coded, there’s no harm in hard-coding the values as
well:

[40000,  60000,  80000, 100000, 120000]

Or we could do this:

>>> numpy.arange(40000, 130000, 20000)
array([ 40000,  60000,  80000, 100000, 120000])

or even just use this:

range(40000, 130000, 20000)

Anything else is just obfuscating the meaning of the code, as you have
learned. Let’s dissect the code:

numpy.arange(130000)
# returns an array from 0 (included) to 130000 (excluded)

numpy.arange(130000)[::20000]
# makes a copy of the array with only every 20-thousandth element
# giving 0, 20000, 40000 etc

numpy.arange(130000)[::20000][2:]
# makes another copy this time skipping the first two elements
# giving 40000, 60000 etc.

Being numpy, it is possibly that the last two steps might not make an
actual copy, it might be what numpy calls a “view”, but don’t worry
about the difference.

Yes, your description makes my confusion clear. About, your point regarding the whole 130000,2000 values come from the dataset and have been set accordingly, but I think to explore further I will have to do some changes and observe the differences.

Thanks by the way!