Count the frequency of an item in a python list

Question

Is there a function in Python that counts the number of occurrences of an item in Python?

Answer 1

I think the function you are looking for is count():

>>> [1,1,2,3,5,6,8,6,3,2,4].count(3)
2

Answer 2

a = [1,1,1,1,2,2,2,2,3,3,4,5,5]
from itertools import groupby
[len(list(group)) for key, group in groupby(a)]

Output:

[4, 4, 2, 1, 2]

Comments

thank you so much. you saved my day. i was really stuck at finding this answer.

Answer 3

import collections
a = [1,1,1,1,2,2,2,2,3,3,4,5,5]
counter=collections.Counter(a)
print(counter)
# Counter({1: 4, 2: 4, 3: 2, 5: 2, 4: 1})
print(counter.values())
# [4, 4, 2, 1, 2]
print(counter.keys())
# [1, 2, 3, 4, 5]
print(counter.most_common(3))
# [(1, 4), (2, 4), (3, 2)]

If you are using Python 2.6 or older, you can download it here.

Hope this helps!!

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Answer 4

To count the number of appearances:

from collections import defaultdict

appearances = defaultdict(int)

for curr in a:
    appearances[curr] += 1

To remove duplicates:

a = set(a) 

Answer 5

Hi, @Everyone,

There are a few functions that can be used to get the frequency of occurrence in a string. So, how do you count frequency in Python?

using list(): Split the string into a list containing the words by using a split function (i.e. string.split()) in python with delimiter space.

using set(): Split the string into a list containing the words by using a split function (i.e. string.split()) in python with delimiter space.
 Use set() method to remove a duplicate and to give a set of unique words

Using a Dictionary

Answer 6

Here is one of the ways to get the number of occurrences when you working with array in python. So, I am sharing one example on how do you count the frequency of an element in an array in Python? 

 Loop through the array and count the occurrence of each element as frequency and store it in another array fr:

1    2   8  3   2   2   2   5   1  

arr = [1, 2, 8, 3, 2, 2, 2, 5, 1];     

#Array fr will store frequencies of element    

fr = [None] * len(arr);    

visited = -1;    

for i in range(0, len(arr)):    

    count = 1;    

    for j in range(i+1, len(arr)):    

        if(arr[i] == arr[j]):    

            count = count + 1;    

            #To avoid counting same element again    

            fr[j] = visited;    

                  if(fr[i] != visited):    

               fr[i] = count;    

     #Displays the frequency of each element present in array    

print("---------------------");    

print(" Element | Frequency");    

print("---------------------");    

for i in range(0, len(fr)):    

    if(fr[i] != visited):    

        print("    " + str(arr[i]) + "    |    " + str(fr[i]));    

print("---------------------");  

Answer 7

Using a dictionary

Here we capture the items as the keys of a dictionary and their frequencies as the values.

list = ['a','b','a','c','d','c','c']
frequency = {}
for item in list:
   if (item in frequency):
      frequency[item] += 1
   else:
      frequency[item] = 1
for key, value in frequency.items():
   print("% s -> % d" % (key, value))

Running the above code gives us the following result −

a -> 2
b -> 1
c -> 3
d -> 1

Answer 8

Given an unsorted list of some elements(may or may not be integers), Find the frequency of each distinct element in the list using a dictionary.

Example:

Input : [1, 1, 1, 5, 5, 3, 1, 3, 3, 1,
                  4, 4, 4, 2, 2, 2, 2]
Output : 1 : 5
         2 : 4
         3 : 3
         4 : 3
         5 : 2
Explanation : Here 1 occurs 5 times, 2 
              occurs 4 times and so on...

# Python program to count the frequency of  # elements in a list using a dictionary    def CountFrequency(my_list):        # Creating an empty dictionary      freq = {}     for item in my_list:         if (item in freq):             freq[item] += 1         else:             freq[item] = 1        for key, value in freq.items():         print ("% d : % d"%(key, value))    # Driver function if __name__ == "__main__":      my_list =[1, 1, 1, 5, 5, 3, 1, 3, 3, 1, 4, 4, 4, 2, 2, 2, 2]        CountFrequency(my_list)

Output:

 1 :  5
 2 :  4
 3 :  3
 4 :  3
 5 :  2

Time Complexity:O(N), where N is the length of the list.