uniquify an array/list with a tolerance in python (uniquetol equivalent)

Question

I want to find the unique elements of an array in a certain range of tolerance

For instance, for an array/list

[1.1 , 1.3 , 1.9 , 2.0 , 2.5 , 2.9]
         


        

Answer 1

In pure Python 2, I wrote the following:

a = [1.1, 1.3, 1.9, 2.0, 2.5, 2.9]                                              

# Per http://fr.mathworks.com/help/matlab/ref/uniquetol.html                                                                                    
tol = max(map(lambda x: abs(x), a)) * 0.3                                       

a.sort()                                                                        

results = [a.pop(0), ]                                                          

for i in a:
    # Skip items within tolerance.                                                                     
    if abs(results[-1] - i) <= tol:                                             
        continue                                                                
    results.append(i)                                                           

print a                                                                         
print results

Which results in

[1.3, 1.9, 2.0, 2.5, 2.9]
[1.1, 2.0, 2.9]

Which is what the spec seems to agree with, but isn't consistent with your example.

If I just set the tolerance to 0.3 instead of max(map(lambda x: abs(x), a)) * 0.3, I get:

[1.3, 1.9, 2.0, 2.5, 2.9]
[1.1, 1.9, 2.5, 2.9]

...which is consistent with your example.