Create a bool list based on a list of float in python

Question

This is a sample_list = [628.6, 628.25, 632.8, 634.65, 634.9, 635.85, 633.55]

I want to create a bool list of true/false based on the condition that if a list value is greater than the previous value, it should be true, else false. In my case, result should be something like this:

mybools = [False,True,True,True,True,False]

how do I do that?

score 0 · Answer 1 · answered Jan 06 '23 at 02:40

0

Use list comprehension:

sample_list = [628.6, 628.25, 632.8, 634.65, 634.9, 635.85, 633.55]
bool_list = [bool(max(sample_list[i-1] - sample_list[i], 0)) 
             for i in range(1, len(sample_list))]

This uses the fact that floats can be cast to boolean values. Anyhint 0 is false, all else is True.

answered Jan 06 '23 at 02:40

Galo do Leste

703
5
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why not just `sample_list[i-1] < sample_list[i]`? – juanpa.arrivillaga Jan 06 '23 at 02:43
Actually that is much neater. Got too clever for my self. Upvote you – Galo do Leste Jan 06 '23 at 02:49
This approach also has potentially unexpected behavior with NaNs. `bool(max(sample_list[i-1] - sample_list[i], 0))` will be True whenever either entry is `NaN`, so you'll get Trues in the output list even though `sample_list[i-1] < sample_list[i]` is False. – Brian61354270 Jan 06 '23 at 02:52

score 0 · Answer 2 · answered Jan 06 '23 at 02:41

Using Numpy, you can accomplish this succinctly by first computing the first-order difference of the input list with numpy.diff, and then inspecting the sign of each entry in the resulting array:

import numpy as np 

sample_list  = [628.6, 628.25, 632.8, 634.65, 634.9, 635.85, 633.55]

mybools = np.diff(sample_list) > 0

print(mybools.tolist())

outputs

[False, True, True, True, True, False]

Create a bool list based on a list of float in python

2 Answers2