CODEWITHSUNDEEP
python-3.x
user13007858
user13007858

Reputation:

Counting how many pairs of numbers in Python list

I searched around and found how to return how many pairs of same value in list. As an example: x = [10,10,20,30,20] => It should return 2 because we have 2 pairs of same value each: (10,10) and (20,20). What is confusing me and do not understand, why the function below is returning result + 1? which leads to wrong output. Output should be 2 but I have 3!! Thank you very much.

x = [20, 30, 20, 30, 20, 40, 30]
freq = {} 
count = 0 
for item in x: 
  if (item in freq): 
     freq[item] += 1
  else:
    freq[item] = 1
for key, value in freq.items(): 
    count+=value/2 
print("Pairs : ",int(count))

Upvotes: 0

Views: 1919

Answers (1)

vbhargav875
vbhargav875

Reputation: 887

The below line of code is not what you are looking for :

set(ar).intersection(mylist)

It just prints out the number of unique elements in your list.

You could do something like this :

freq = {}
count = 0 
for item in x: 
    if (item in freq): 
        freq[item] += 1
    else: 
        freq[item] = 1

for key, value in freq.items(): 
    count+=value/2
print("Pairs : ",count)

Upvotes: 1

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