Question

i apologize in advance for not being very precise, as a i dont know the mathematical expression for what i want.

i am using matplotlib to analyze a large dataset. What i have now is a distribution of x,y points. I want to find out the cases in which the x values of my function are the same, but y differs the greatest. So if i plot it, one part of the cases is at the top of my graph, the other is the botton of the graph.

So how do i get the points(x,y), (x,y’) where f(x)=y and f(x)=y’ and y-y’=max ?

cheers

Answer 1

Not sure if I understand correctly but here is a raw solution which you could adapt:

from collections import defaultdict

input = [(1.2,2), (1.2, 6), (1.2, -2), (2,8), (2,7), (2,18)]

indices_dict = defaultdict(lambda: list([[], []]))

for idx, val in enumerate(input):
    indices_dict[val[0]][0].append(idx)
    indices_dict[val[0]][1].append(val[1])

for key in indices_dict:
    y_values = indices_dict[key][1]
    idx_values =  indices_dict[key][0]
    max_idx = idx_values[y_values.index(max(y_values))]
    min_idx = idx_values[y_values.index(min(y_values))]
    print 'Max diff for x=%s is found between points %s and %s' %(key, input[min_idx], input[max_idx])

This should print for each distinct x the points which have the max difference on y. You can adapt it to your requirements.