# Python | Summation of Non-Zero groups

Many times we need to get the summation of not the whole list but just a part of it and at regular intervals. These intervals are sometimes decided statically before traversal, but sometimes, the constraint is more dynamic and hence we require to handle it in more complex way. Criteria discussed here is summation of non-zero groups. Let’s discuss certain ways in which this task can be done.

Method #1 : Using loops

This task can be performed using the brute force manner using the loops. We just traverse the list each element to test for it’s succeeding element to be non-zero value and perform the summation once we find a next value to be zero and append it in result list.

 `# Python3 code to demonstrate ` `# summation of non-zero groups ` `# Using loops ` ` `  `# initializing list ` `test_list ``=` `[``4``, ``9``, ``0``, ``0``, ``3``, ``4``, ``5``, ``0``, ``0``, ``4``, ``0``] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using loops ` `# summation of non-zero groups ` `res ``=` `[] ` `val ``=` `0` `for` `ele ``in` `test_list: ` `    ``if` `ele ``=``=` `0``: ` `        ``if` `val !``=` `0``: ` `            ``res.append(val) ` `            ``val ``=` `0` `    ``else``: ` `        ``val ``+``=` `ele ` ` `  `# print result ` `print``(``"The non-zero group summation of list is : "` `+` `str``(res)) `

Output :

```The original list : [4, 9, 0, 0, 3, 4, 5, 0, 0, 4, 0]
The non-zero group summation of list is : [13, 12, 4]
```

Method #2 : Using `itertools.groupby() + sum()`

This particular task can also be performed using groupby function to group all the non-zero values and sum function can be used to perform their summation.

 `# Python3 code to demonstrate ` `# summation of non-zero groups ` `# Using itertools.groupby() + sum() ` `from` `itertools ``import` `groupby ` ` `  `# initializing list ` `test_list ``=` `[``4``, ``9``, ``0``, ``0``, ``3``, ``4``, ``5``, ``0``, ``0``, ``4``, ``0``] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using itertools.groupby() + sum() ` `# summation of non-zero groups ` `res ``=` `[``sum``(val) ``for` `keys, val ``in` `groupby(test_list, ` `              ``key ``=` `lambda` `x: x !``=` `0``) ``if` `keys !``=` `0``] ` ` `  `# print result ` `print``(``"The non-zero group summation of list is : "` `+` `str``(res)) `

Output :

```The original list : [4, 9, 0, 0, 3, 4, 5, 0, 0, 4, 0]
The non-zero group summation of list is : [13, 12, 4]
```

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