CODEWITHSUNDEEP
pythondictionarytuples
MLister
MLister

Reputation: 10300

Return the largest value of a given element of tuple keys in a dictionary

I have a dict with tuples as keys, and I want to obtain the largest value available, say for the second element of the tuple keys currently in the dictionary. For example, given:

my_dict = {('a', 1):value_1, ('b', 1):value_2, ('a', 2):value_3, ('c', 3):value_4, ('b', 2):value_5}

so the largest value for the second elements of the keys is 3.

What is the fastest way to derive this value?

Upvotes: 1

Views: 1506

Answers (3)

Joel Cornett
Joel Cornett

Reputation: 24788

Either:

largest_key = max(my_dict, key=lambda x: x[1])

Or:

from operator import itemgetter
largest_key = max(my_dict, key=itemgetter(1))

According to DSM, iterating over a dict directly is faster than retrieving and iterating over keys() or viewkeys().

What I think Ms. Zverina is talking about is converting your data structure from a dict with tuple keys to something like this:

my_dict = {
    'a': {
            1: value_1,
            2: value_3
         }
    'b': {
            1: value_2,
            2: value_5
         }
    'c': {
            3: value_4
         }
}

That way, if you wanted find the max of all values with a, you could simply do:

largest_key = max(d['a'])

At no extra cost. (Your data is already divided into subsets, so you don't have to waste computation on building subsets each time you do a search).

EDIT

To restrict your search to a given subset, do something like this:

>>> subset = 'a'
>>> largest_key_within_subset = max((i for i in my_dict if i[0] == subset), key=itemgetter(1))

Where (i for i in my_dict if i[0] == subset) is a generator that returns only keys that are in the given subset.

Upvotes: 5

ddzialak
ddzialak

Reputation: 1080

If you have no additional information about any relation between elements in any set (like keys in dictionary in that case) then you have to check each element => complexity O(n) (linear) - the only improvement can be using some build-in function like max

If you need quite often to obtain (or pop) max value then think about different structure (like heap).

Upvotes: 1

Maria Zverina
Maria Zverina

Reputation: 11163

If you looking for largest value i.e. 3 use this:

print max(my_dict.keys(), key = lambda x: x[1])[1]

If you are looking for largest value from the dict, use this:

my_dict = {('a', 1):'value_1', ('b', 1):'value_2', ('a', 2):'value_3', ('c', 3):'value_4', ('b', 2):'value_5'}

largest = max(my_dict.keys(), key = lambda x: x[1])
print my_dict[largest]

Upvotes: 1

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