Python - Prefix frequency in string List

Sometimes, while working with Python lists, we can have a problem in which we need to get the count of strings that start with particular substring. This can have an application in web development and general programming. Lets discuss certain ways in which this task can be performed.

Method #1 : Using loop + startswith()
The combination of above functions can be used to perform this task. In this, we run a loop for each string in list and employ startswith() to get the strings that start with particular prefix.

# Python3 code to demonstrate  
# Prefix frequency in List 
# using loop + startswith() 
  
# Initializing list 
test_list = ['gfgisbest', 'geeks', 'gfgfreak', 'gfgCS', 'Gcourses'] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# Initializing substring 
test_sub = 'gfg'
  
# Prefix frequency in List 
# using loop + startswith() 
res = 0
for ele in test_list: 
    if ele.startswith(test_sub): 
        res = res + 1
              
# printing result  
print ("Strings count with matching frequency : " + str(res)) 

Output :

The original list is : [‘gfgisbest’, ‘geeks’, ‘gfgfreak’, ‘gfgCS’, ‘Gcourses’]
Strings count with matching frequency : 3

Method #2 : Using sum() + startswith()
The combination of above functions can be used to perform this task. In this, we perform the task of counting using sum() and startswith(), is used to perform task of checking of prefix.

# Python3 code to demonstrate  
# Prefix frequency in List 
# using sum() + startswith() 
  
# Initializing list 
test_list = ['gfgisbest', 'geeks', 'gfgfreak', 'gfgCS', 'Gcourses'] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# Initializing substring 
test_sub = 'gfg'
  
# Prefix frequency in List 
# using sum() + startswith() 
res = sum(sub.startswith(test_sub) for sub in test_list) 
              
# printing result  
print ("Strings count with matching frequency : " + str(res)) 

Output :

The original list is : [‘gfgisbest’, ‘geeks’, ‘gfgfreak’, ‘gfgCS’, ‘Gcourses’]
Strings count with matching frequency : 3

My Personal Notes

Python – Prefix frequency in string List

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