Identify duplicate values in a list in Python

Question

Is it possible to get which values are duplicates in a list using python?

I have a list of items:

    mylist = [20, 30, 25, 20]

I k

Answer 1

You should sort the list:

mylist.sort()

After this, iterate through it like this:

doubles = []
for i, elem in enumerate(mylist):
    if i != 0:
        if elem == old:
            doubles.append(elem)
            old = None
            continue
    old = elem

Answer 2

The following list comprehension will yield the duplicate values:

[x for x in mylist if mylist.count(x) >= 2]

Answer 3

The following code will fetch you desired results with duplicate items and their index values.

  for i in set(mylist):
    if mylist.count(i) > 1:
         print(i, mylist.index(i))

Answer 4

You can use list compression and set to reduce the complexity.

my_list = [3, 5, 2, 1, 4, 4, 1]
opt = [item for item in set(my_list) if my_list.count(item) > 1]

Answer 5

You can print duplicate and Unqiue using below logic using list.

def dup(x):
    duplicate = []
    unique = []
    for i in x:
        if i in unique:
            duplicate.append(i)
        else:
            unique.append(i)
    print("Duplicate values: ",duplicate)
    print("Unique Values: ",unique)

list1 = [1, 2, 1, 3, 2, 5]
dup(list1)

Answer 6

m = len(mylist)
for index,value in enumerate(mylist):
        for i in xrange(1,m):
                if(index != i):
                    if (L[i] == L[index]):
                        print "Location %d and location %d has same list-entry:  %r" % (index,i,value)

This has some redundancy that can be improved however.