Numpy: A new tremandous BUG in Advanced Indexing?

[Levstyle]

This is a BUG

train = np.zeros([26,26])
train2 = np.zeros([26,26])
tmp = [1,2,3,4,5,6,1,2,3,4,5,6]
train[tmp[0:-1], tmp[1:]] += 1
for i in range(len(tmp)-1):
    train2[tmp[i], tmp[i+1]] += 1
print(np.sum(train - train2))

the output is -5
I find that train is not equal to train2 when there are some duplicate tuples in tmp. Is there something wrong in numpy slicing.

[RogerMonkey]

The same to you.

[MSeifert04]

You know that you're trying to write to the "same position" twice, for example [1, 2]. Unfortunatly (or fortunatly, depending on the point of view) that doesn't work.

But you can use np.add.at which according to the docs "For addition ufunc, this method is equivalent to a[indices] += b, except that results are accumulated for elements that are indexed more than once.":

train = np.zeros([26,26])
np.add.at(train, [tmp[:-1], tmp[1:]], 1)

[Levstyle]

Thanks!