In Python, how do you find the index of the first value greater than a threshold in a sorted list?

python algorithm search bisection
static_rtti picture static_rtti · Sep 2, 2011 · Viewed 18.4k times · Source

In Python, how do you find the index of the first value greater than a threshold in a sorted list?

I can think of several ways of doing this (linear search, hand-written dichotomy,..), but I'm looking for a clean an reasonably efficient way of doing it. Since it's probably a pretty common problem, I'm sure experienced SOers can help!

Thanks!

Answer

eumiro picture eumiro · Sep 2, 2011

Have a look at bisect.

import bisect

l = [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

bisect.bisect(l, 55) # returns 7

Compare it with linear search:

timeit bisect.bisect(l, 55)
# 375ns


timeit next((i for i,n in enumerate(l) if n > 55), len(l))
# 2.24us


timeit next((l.index(n) for n in l if n > 55), len(l))
# 1.93us

Related questions

How to implement a binary tree?

Which is the best data structure that can be used to implement a binary tree in Python?

Read More
Removing duplicates in the lists

Pretty much I need to write a program that checks if a list has any duplicates and if it does it removes them and returns a new list with the items that weren't duplicated/removed. This is what I have …

Read More
How to generate all permutations of a list?

How do you generate all the permutations of a list in Python, independently of the type of elements in that list? For example: permutations([]) [] permutations([1]) [1] permutations([1, 2]) [1, 2] [2, 1] permutations([1, 2, 3]) [1, 2, 3] [1, 3, 2] [2, 1, 3] [2, 3, 1] [3, 1, 2] [3, 2, 1]

Read More