How to check efficiently numpy array contains item within given range?

Question

I have a numpy array, called a , I want to check whether it contains an item in a range, specified by two values.

import numpy as np
a = np.arange(100)

mintrshold=33
maxtreshold=66

My solution:

goodItems = np.zeros_like(a)
goodItems[(a<maxtreshold) & (a>mintrshold)] = 1

if goodItems.any(): 
   print (there s an item within range)

Can you suggest me a more effective, pythonic way?

I don't know about numpy per se, but with normal python list I'd write it like; if any(mintrshold < x <= maxtreshold for x in a): print('True') — EzzatA
– EzzatA, Commented May 31, 2017 at 10:25
Since you are interested in finding if any item exists: as a general recommendation, use a generator expression with any if you expect to find a valid item early in the array - being able to return True without iterating through the whole array can save a lot of runtime. Use a numpy expression with .any() if you don't expect an item early or at all. Always benchmark with real data. — bers
– bers, Commented Aug 7, 2023 at 5:37
Does this answer your question? Numpy: find index of the elements within range — bers
– bers, Commented Aug 7, 2023 at 20:53

Slam · Accepted Answer · 2017-05-31 10:31:22Z

10

Numpy arrays doesn't work well with pythonic a < x < b. But there's func for this:

np.logical_and(a > mintrshold, a < maxtreshold)

or

np.logical_and(a > mintrshold, a < maxtreshold).any()

in your particular case. Basically, you should combine two element-wise ops. Look for logic funcs for more details

answered May 31, 2017 at 10:31

Slam

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1 Comment

user3598726 Over a year ago

Thank you, it is more elegant and 2.5 times faster than my naive solution.

gold_cy · Accepted Answer · 2017-05-31 10:33:53Z

2

Adding to the pure Numpy answer we can also use itertools

import itertools

bool(list(itertools.ifilter(lambda x: 33 <= x <= 66, a)))

For smaller arrays this would suffice:

bool(filter(lambda x: 33 <= x <= 66, a))

answered May 31, 2017 at 10:33

gold_cy

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7 Comments

user3598726 Over a year ago

I tried your second line, but it does not work, always ends up being True

gold_cy Over a year ago

I thought that was the desired output, to return True if numbers in the array do fall within the condition. If you need list/array of bools returned let me know and I can modify it for that.

user3598726 Over a year ago

You interpreted my question well,but if a=np.arange(100,120), your second line still returns True

gold_cy Over a year ago

It returns False for me, I think maybe you are copying or typing something incorrectly. Both of my one-liners return False given that a=np.arange(100,120)

user3598726 Over a year ago

I tried your second oneliner with pyton 3.6, it returns True, in python 2.5 it returns False (a=np.arange(100,120)):D. I only checked it with 3.6 only yesterday.

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