Explain Python's slice notation. In short, the colons (:) in subscript notation (subscriptable[subscriptarg]) make slice notation, which has the optional arguments start, stop, and step: sliceable[start:stop:step] Python slicing is a computationally fast way to methodically access parts of your data.

Aug 10, 2010 · We can then open up slice objects as: s = slice(1, 2, 3) assert s.start == 1 assert s.stop == 2 assert s.step == 3 This is notably used in Numpy to slice multi-dimensional arrays in any direction. Of course, any sane API should use ::3 with the usual "every 3" semantic. The related Ellipsis is covered further at: What does the Ellipsis object do?

Python interpreter is smart enough to convert a slice of range into another range. This is an optimization, ranges are generators. They are dynamic, i.e. they don't hold all the elements in the memory at once. It the interpreter you are using worked step-by-step, it would have to generate whole list, just to be able to iterate in a reverse order.

For additional ways, read this: How do I get time of a Python program's execution? One can also adjust the previous options to a lambda function, such as the following df_new = df.apply(lambda x: x[:10]) # or df_new = df.apply(lambda x: x.head(10))

Dec 17, 2021 · To trim in-place, use del on a slice; e.g. del listobj[-x:] will remove the last x elements from the list object. – Martijn Pieters Commented Aug 18, 2016 at 14:09

May 19, 2012 · I load some machine learning data from a CSV file. The first 2 columns are observations and the remaining columns are features. Currently, I do the following: data = pandas.read_csv('mydata.csv')...

This is Python 2 syntax, in Python 3 use d.keys(). This still uses a loop, but at least the dictionary comprehension is a lot more readable. Using set intersections is very efficient, even if d or l is large.

May 10, 2011 · python -m pip install image_slicer Copy the image you want to slice into the Python root directory, open a python shell (not the "command line"), and enter these commands: import image_slicer image_slicer.slice('huge_test_image.png', 14) The beauty of this module is that it . Is installed in python ; Can invoke an image split with two lines of code

Feb 27, 2023 · To slice a multi-dimensional array, the dimension (i.e. axis) must be specified. As OP noted, arr[i:j][i:j] is exactly the same as arr[i:j] because arr[i:j] sliced along the first axis (rows) and has the same number of dimensions as arr (you can confirm by arr[i:j].ndim == arr.ndim); so the second slice is still slicing along the first dimension (which was already done by the first slice).

Aug 9, 2012 · It's worth a quick note that despite the notational similarity between df.loc[1:3] and some_list[1:3], the first uses an inclusive upper index while the second (and most of python) uses an exclusive upper index. –