How to check if two keys in dictionary hold the same value

Question

This seems like such an obvious thing that I feel like I'm missing out on something, but how do you find out if two different keys in the same dictionary have the exact same value? For example, if you have the dictionary test with the keys a, b, and c and the keys a and b both have the value of 10, how would you figure that out? (For the point of the question, please assume a large number of keys, say 100, and you have no knowledge of how many duplicates there are, if there are multiple sets of duplicates, or if there are duplicates at all). Thanks.

Answer 1

len(dictionary.values()) == len(set(dictionary.values()))

This is under the assumption that the only thing you want to know is if there are any duplicate values, not which values are duplicates, which is what I assumed from your question. Let me know if I misinterpreted the question.

Basically this is just checking if any entries were removed when the values of the dictionary were casted to an object that by definition doesn't have any duplicates.

If the above doesn't work for your purposes, this should be a better solution:

set(k for k,v in d.items() if d.values().count(v) > 1))

Basically the second version just checks to see if there is more than one entry that will be removed if you try popping it out of the list.

Answer 2

keys = set()
for key1 in d:
    for key2 in d:
        if key1 == key2: continue
        if d[key1] == d[key2]:
            keys |= {key1, key2}

i.e. that's Θ(n²) what you want. The reason is that a dict does not provide Θ(1) search of a key, given a value. So better rethink your data structure choices if that's not good enough.

Answer 3

You can use list in conjunction with dictionary to find duplicate elements! Here is a simple code demonstrating the same:

d={"val1":4,"val2":4,"val3":5,"val4":3}
l=[]
for key in d:
      l.append(d[key])
      l.sort()
print(l)
for i in range(len(l)):
    if l[i]==l[i+1]:
        print("true, there are duplicate elements.")
        print("the keys having duplicate elements are: ")
        for key in d:
            if d[key]==l[i]:
                print(key)
        break

output:

runfile('C:/Users/Andromeda/listeqtest.py', wdir='C:/Users/Andromeda')

[3, 4, 4, 5]
true, there are duplicate elements.
the keys having duplicate elements are: 
val1
val2

when you sort the elements in the list, you will find that equal values always appear together!