How to index without triggering 'IndexError: invalid index to scalar variable.' error

Question

I am trying to find the maximum value(s) in a dictionary and my approach is to iterate through and check for the greatest values and make a list of the greatest value/key pair and anything equivelent to it from a dictionary and I have the following...

def foo(class_sum, input_object):  # Predicts the class x is a member of given probability dictionary
    probabilities = calc_class_probs(class_sum, input_object)  # Returns a dictionary with probability elements
    best_label, best_perc = list(), list()
    best_perc.append(-1)
    print(best_perc[0])
    for val in probabilities:
        print(probabilities[val])
        if probabilities[val] > best_perc[0]:
            del best_label
            del best_perc  # Empty list in case unwanted elements are present
            best_label, best_perc = val, probabilities[val]  # update with new best
        elif probabilities[val] == best_perc:
            best_label.append(val)
            best_perc.append(probabilities[val])

    return best_label, best_perc

So from this I expect that if probabilities[val] > best_perc[0]: will evaluate to 7.591391076586993e-36 > -1, at least for the first iteration. However I get the following output from the print statements...

-1
7.591391076586993e-36

EDIT: it appears to fail on the second iteration, could this be due to the del statements?

0 7.591391076586993e-36
1 7.297754873023128e-36
...
IndexError: invalid index to scalar variable.

and this error...

if probabilities[val] > best_perc[0]:
IndexError: invalid index to scalar variable.

Why can it print the values but not index them here? Please note probabilities is a dictionary with keys that have single probability values like the below.

{'0': 7.59139e-36, '1': 7.2977e-36,...}

Relandom · Accepted Answer · 2019-05-05 20:54:56Z

2

I believe your problem is here:

best_label, best_perc = val, probabilities[val]

After executing first 'if' best_lavel and best_perc is no longer list, so you cant access best_perc[0].

You can replace it by

best_label, best_perc = [val], [probabilities[val]]

Notice, when you iterate in a dictionary, you iterate through keys, not values. You can alos iterate by keys and values:

for key, val in dictionary.items():

edited May 5, 2019 at 20:54

answered May 5, 2019 at 20:37

Relandom

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1 Comment

Legion Daeth Over a year ago

Thanks for the tip about iterating through dictionaries, solved and improved my code!

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