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Python | Sectional subset sum in list
• Last Updated : 20 Mar, 2019

Some of the classical problems in programming domain comes from different categories and one among them is finding the sum of subsets. This particular problem is also common when we need to accumulate the sum and store consecutive group summation. Let’s try different approaches to this problem in python language.

Method #1 : Using list comprehension + `sum()`
The list comprehension can be used to perform the this particular task to filter out successive groups and sum function can be used to get the summation of the filtered solution.

 `# Python3 code to demonstrate ` `# Sectional subset sum in list  ` `# using list comprehension + sum() ` ` `  `# initializing list ` `test_list ``=` `[``4``, ``7``, ``8``, ``10``, ``12``, ``15``, ``13``, ``17``, ``14``] ` ` `  `# printing original list  ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using list comprehension + sum() ` `# Sectional subset sum in list  ` `res ``=` `[ ``sum``(test_list[x : x ``+` `3``])  ` `       ``for` `x ``in` `range``(``0``, ``len``(test_list), ``3``)] ` ` `  `# printing result ` `print``(``"The grouped summation list is : "` `+` `str``(res)) `

Output :

```The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14]
The grouped summation list is : [19, 37, 44]
```

Method #2 : Using `sum() + itertools.islice()`
The task of slicing the list into chunks is done by islice method here and the conventional task of getting the summation is done by the sum function as the above method.

 `# Python3 code to demonstrate ` `# Sectional subset sum in list  ` `# using itertools.islice() + sum() ` `import` `itertools ` ` `  `# initializing list ` `test_list ``=` `[``4``, ``7``, ``8``, ``10``, ``12``, ``15``, ``13``, ``17``, ``14``] ` ` `  `# printing original list  ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using itertools.islice() + sum() ` `# Sectional subset sum in list  ` `res ``=` `[``sum``(``list``(itertools.islice(test_list, i, i ``+` `3``))) ` `                  ``for` `i ``in` `range``(``0``, ``len``(test_list), ``3``)] ` ` `  `# printing result ` `print``(``"The grouped summation list is : "` `+` `str``(res)) `

Output :

```The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14]
The grouped summation list is : [19, 37, 44]
```

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