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Python – Sum elements matching condition

  • Last Updated : 29 Dec, 2019

Checking a number/element by a condition is a common problem one faces and is done in almost every program. Sometimes we also require to get the totals sum that match the particular condition to have a distinguish which to not match for further utilization. Lets discuss certain ways in which this task can be achieved.

Method #1 : Using loop
This is brute force method to perform this particular task. In this, we iterate list, find elements that match a particular condition and take sum.




# Python 3 code to demonstrate 
# Sum elements matching condition
# using loop
  
# initializing list
test_list = [3, 5, 1, 6, 7, 9]
  
# printing original list
print ("The original list is : " + str(test_list))
  
# using loop
# Sum elements matching condition
# checks for odd
res = 0
for ele in test_list:
    if ele % 2 != 0:
        res = res + ele 
          
# printing result
print ("The sum of odd elements: " + str(res))
Output :
The original list is : [3, 5, 1, 6, 7, 9]
The sum of odd elements: 25

 

Method #2 : Using sum() + generator expression
This method uses the trick of adding elelement to the sum whenever the generator expression returns true. By the time list gets exhausted, summation of numbers matching a condition is returned.






# Python 3 code to demonstrate 
# Sum elements matching condition
# using sum() + generator expression
  
# initializing list
test_list = [3, 5, 1, 6, 7, 9]
  
# printing original list
print ("The original list is : " + str(test_list))
  
# using sum() + generator expression
# Sum elements matching condition
# checks for odd
res = sum(i for i in test_list if i % 2 != 0)
  
# printing result
print ("The sum of odd elements: " + str(res))
Output :
The original list is : [3, 5, 1, 6, 7, 9]
The sum of odd elements: 25

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