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I've seen a lot of variations of this question from things as simple as remove duplicates to finding and listing duplicates. Even trying to take bits and pieces of these examples does not get me my result.

My question is how am I able to check if my list has a duplicate entry? Even better, does my list have a non-zero duplicate?

I've had a few ideas -

#empty list
myList = [None] * 9 

#all the elements in this list are None

#fill part of the list with some values
myList[0] = 1
myList[3] = 2
myList[4] = 2
myList[5] = 4
myList[7] = 3

#coming from C, I attempt to use a nested for loop
j = 0
k = 0
for j in range(len(myList)):
    for k in range(len(myList)):
        if myList[j] == myList[k]:
            print "found a duplicate!"

If this worked, it would find the duplicate (None) in the list. Is there a way to ignore the None or 0 case? I do not care if two elements are 0.

Another solution I thought of was turn the list into a set and compare the lengths of the set and list to determine if there is a duplicate but when running set(myList) it not only removes duplicates, it orders it as well. I could have separate copies, but it seems redundant.

Try changing the actual comparison line to this:

if myList[j] == myList[k] and not myList[j] in [None, 0]:

How do I check if there are duplicates in a flat list?, How do I check if there are duplicates in a flat list? python string list duplicates. For example, given the list ['one', 'two', 'one']  def list_duplicates(seq): seen = set() seen_add = seen.add # adds all elements it doesn't know yet to seen and all other to seen_twice seen_twice = set( x for x in seq if x in seen or seen_add(x) ) # turn the set into a list (as requested) return list( seen_twice ) a = [1,2,3,2,1,5,6,5,5,5] list_duplicates(a) # yields [1, 2, 5]

I'm not certain if you are trying to ascertain whether or a duplicate exists, or identify the items that are duplicated (if any). Here is a Counter-based solution for the latter:

# Python 2.7
from collections import Counter

# Rest of your code

counter = Counter(myList)
dupes = [key for (key, value) in counter.iteritems() if value > 1 and key]
print dupes

The Counter object will automatically count occurances for each item in your iterable list. The list comprehension that builds dupes essentially filters out all items appearing only once, and also upon items whose boolean evaluation are False (this would filter out both 0 and None).

If your purpose is only to identify that duplication has taken place (without enumerating which items were duplicated), you could use the same method and test dupes:

if dupes:  print "Something in the list is duplicated"

How do I find the duplicates in a list and create another list with them , To compute the list of duplicated elements without libraries: 'test.thg435(test.l)' 1000 loops, best of 3: 266 usec per loop $ python -mtimeit -s 'import test' 'test. As can be seen from the code above, we create a list called lst1 containing various numbers and an empty set called duplicates, which we’ll use to store the duplicate values. To find the duplicates in list1 we’ll make sure we copy the values only once inside the duplicates set with the help of the not in instruction.

If you simply want to check if it contains duplicates. Once the function finds an element that occurs more than once, it returns as a duplicate.

my_list = [1, 2, 2, 3, 4]

def check_list(arg):
    for i in arg:
        if arg.count(i) > 1:
            return 'Duplicate'

print check_list(my_list) == 'Duplicate' # prints True

how to check if there are duplicates in a list python Code Example, Get code examples like "how to check if there are duplicates in a list python" instantly right from your google search results with the Grepper  and you can also list the duplicates itself (may contain duplicates again as in the example): [z [i] for i in range (len (z)) if not i == z.index (z [i])] >>> ['a', 'b', 'a']

To remove dups and keep order ignoring 0 and None, if you have other falsey values that you want to keep you will need to specify is not None and not 0:

print [ele for ind, ele in enumerate(lst[:-1]) if ele not in lst[:ind] or not ele] 

If you just want the first dup:

for ind, ele in enumerate(lst[:-1]):
    if ele in lst[ind+1:] and ele:

Or store seen in a set:

seen = set()
for  ele in lst:
    if ele in seen:
    if ele:

Python, Python | Program to print duplicates from a list of integers Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button  To just determine if there are any duplicates in the original list: from collections import Counter def has_dupes(l): # second element of the tuple has number of repetitions return Counter(l).most_common()[0][1] > 1 Or to get a list of items that have duplicates: def get_dupes(l): return [k for k, v in Counter(l).items() if v > 1]

You can use collections.defaultdict and specify a condition, such as non-zero / Truthy, and specify a threshold. If the count for a particular value exceeds the threshold, the function will return that value. If no such value exists, the function returns False.

from collections import defaultdict

def check_duplicates(it, condition, thresh):
    dd = defaultdict(int)
    for value in it:
        dd[value] += 1
        if condition(value) and dd[value] > thresh:
            return value
    return False

L = [1, None, None, 2, 2, 4, None, 3, None]

res = check_duplicates(L, condition=bool, thresh=1)  # 2

Note in the above example the function bool will not consider 0 or None for threshold breaches. You could also use, for example, lambda x: x != 1 to exclude values equal to 1.

Python Remove Duplicates from a List, We can use not in on list to find out the duplicate items. We create a result list and insert only those that are not already not in. If we want to compare rows & find duplicates based on selected columns only then we should pass list of column names in subset argument of the Dataframe.duplicate () function. It will select & return duplicate rows based on these passed columns only. For example let’s find & select rows based on a single column,

What is the python program for finding duplicate element from a list , [2,4,10,20,5]. So , Here is the Simplest Code to find the duplicate number in the list Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. With Python ≥3.8, check for duplicates and access

Python Remove Duplicates From List, Some approaches may lead to the elements becoming reordered, but this is not necessary. Methods. We use a for-loop and check a set and append to a new list​  Python | Program to print duplicates from a list of integers Given a list of integers with duplicate elements in it. The task to generate another list, which contains only the duplicate elements.

Python: Remove duplicates from a list, Write a Python program to remove duplicates from a list. Example - 1 : Python: Medium Hard. Test your Python skills with w3resource's quiz. By Using Set. This is the most popular way of removing duplicates from list. A set is an unordered collection of data type that is mutable. set () automatically removes duplicates. list1 = [9,9,5,6,3,4,1,9,2,4,2] list2 = list (set (list1)) print ("New List : ", list2) Now let’s check the output.

  • You're on the right track! I would definitely recommend the set operation, as it's a single function call that gets exactly what you need; you can then pop out the Nones and 0s from your final set.
  • Regular sets in Python lack a defined order, but there is always OrderedDict
  • return outside of function = syntax error
  • You'd also want to check that you aren't comparing an index against itself and also that you don't derive 2 duplicates for both times you compare the indexes (e.g. dont count 2 duplicates because 3 is a duplicate of 4 but 4 is also a duplicate of 3)
  • "Is there a way to ignore the None or 0 case?" Sure: if myList[i] is None or myList[i] == 0: continue
  • Thank you, but what if I wanted the second duplicate?
  • @MikeIssa, so the second occurrence? It would only really make sense of you wanted the index or to reorder based on when the second appeared, if you had a concrete example, it would be easy to implement, with a collections.Counter
  • Please consider explaining your answer.
  • How does this tell you if any of the truthy elements are duplicated?