如何从python列表中获取值的范围？

Question

I'd like to do the following Matlab code:

indexes=find(data>0.5);
data2=data(indexes(1):indexes(length(indexes))+1);

in Python, so I did:

indexes=[x for x in data if x>0.5]
init=indexes[1]
print(indexes)
end=indexes[len(indexes)]+1
data2=data[init:end]

but I'm getting this error:

end=indexes[len(indexes)]+1 IndexError: list index out of range

I think the indexes in Python may not be the same ones as I get in Matlab?

Answer 1

Your list comprehension isn't building a list of indices, but a list of the items themselves. You should generate the indices alongside the items using enumerate :

ind = [i for i, x in enumerate(data) if x > 0.5]

And no need to be so verbose with slicing:

data2 = data[ind[0]: ind[-1]+1] # Matlab's index 1 is Python's index 0

Indexing the list of indices with len(ind) will give an IndexError as indexing in Python starts from 0 (unlike Matlab) and the last index should be fetched with ind[len(ind)-1] or simply ind[-1] .

Answer 2

len(indexes) will give you the index of the last element of the list, so that value plus 1 is out of the range of the list.

It looks like what you're trying to do is find the indices of the list that have values of greater that 0.5 and put those values into data2 . This is better suited to a numpy array.

import numpy as np
data2 = data[data > 0.5]