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Python | Count the sublists containing the given item in the list

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Examples :

  Input:  lst = [1, 3, 5], [1, 3, 5, 7], [1 , 3, 5, 7, 9]] x = 1  Output:  3  Input:  lst = ([’a’], [’ a’, ’c’, ’b’], [’ d’]) x = ’a’  Output:  2 

Approach # 1: Naive Approach

Count the number of lists containing x . Initialize counter to 0, then run a for loop and check if x exists in each list or not. If so, increase the counter .

# Python3 Counting program
# a list containing a specific element
# in a list of lists

  

def countList (lst, x):

count = 0

for i in range ( len (lst)):

if x in lst [i]:

count + = 1

 

return count

  
Driver code

lst = ( [ ’a’ ], [ ’ a’ , ’c’ , ’ b’ ], [ ’d’ ]) 

x = ’a’

 

print (countList (lst, x))

Exit :

 2 

Approach # 2: Understanding the list (Alternative for the naive)
A simple one-line list comprehension can also help by simply converting the above naive approach to a one-line loop.

# Python3 Program for counting numbers
# a list containing a specific element
# in a list of lists

 

def countList ( lst, x):

 

return sum (x in item for item in lst)

  
Driver code

lst = ([ ’a’ ], [ ’a’ , ’ c’ , ’b’ ], [ ’ d’ ]) 

x = ’a’

print (countList (lst, x ))

Exit:

 2 

Approach # 3:  Using chain.from_iterable () and Counter

We can use Counter to count the number of "x" lists. Since we don’t want to count "x" more than once for each inner list, we convert each inner list to sets. Then combine these sets of elements into one sequence using chain.from_iterable () .

# Python3 Counting program
# a list containing a specific element
# in a list of lists

from itertools import chain

from collections import Counter

 

def countList (lst, x):

 

return Counter (chain.from_iterable ( set (i) for i in lst)) [x]

 
Driver code

lst = ([ ’a’ ], [ ’a’ , ’ c’ , ’b’ ], [ ’d’ ]) 

x = ’a’

print (countList (lst, x))

Exit :

 2 

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