Welcome to Software Development on Codidact!
Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.
How do I trim a sorted list in Python?
How do I trim a sorted list in Python, so that I only keep the elements greater than a certain value?
For example, if I have this list:
l = [1, 3, 5, 6, 7, 8]
How can I efficiently get a list of numbers greater than 4?
3 answers
You can use the functions in the bisect module with a list slicing operator. For example bisect_left finds the index of the insertion point in a sorted list, and if the values are equal, it will find the position to its left.
>>> l = [1, 3, 5, 6, 7, 8]
>>> from bisect import bisect_left
>>> bisect_left(l, 4)
2
>>> bisect_left(l, 5)
2
>>> l[bisect_left(l, 4):]
[5, 6, 7, 8]
>>> l[bisect_left(l, 5):]
[5, 6, 7, 8]
0 comment threads
The library module itertools provides a function called dropwhile().
The example they give is:
dropwhile(lambda x: x<5, [1,4,6,3,8])
→ 6 3 8
So, to get a list of numbers greater than 4, drop items while they are less than or equal to 4:
import itertools
l = [1, 3, 5, 6, 7, 8]
result = itertools.dropwhile(lambda x: x<=4, l)
Note that result at this point will be a lazy iterator object of some kind, not an actual list. So you might have to do: print(*result) to confirm it works. But you can iterate it, or call list(result) to make it a true list. (Remember, also, that iterators get consumed.)
0 comment threads