Summation of elements in list can be performed using many inbuilt function. Normal summation functions have many applications in various domains. This article discusses to sum just the first N occurrences of elements matching particular condition.

**Method #1 : Naive Method**

We can sum the elements that are matching condition, after N occurrences of elements have been done and we can stop the operation. Code below demonstrates the same.

`# Python 3 code to demonstrate ` `# Summation of first N matching condition` `# using Naive Method ` ` ` `# initializing list` `test_list ` `=` `[` `3` `, ` `5` `, ` `1` `, ` `6` `, ` `7` `, ` `9` `, ` `8` `, ` `5` `]` ` ` `# printing original list` `print` `(` `"The original list is : "` `+` `str` `(test_list))` ` ` `# using Naive Method ` `# Summation of first N matching condition` `# sums first 3 odd occurrences` `counter ` `=` `1` `res ` `=` `0` `for` `i ` `in` `test_list:` ` ` `if` `counter <` `=` `3` `and` `(i ` `%` `2` `!` `=` `0` `):` ` ` `res ` `=` `res ` `+` `i` ` ` `counter ` `=` `counter ` `+` `1` ` ` `# printing result` `print` `(` `"The filtered list is : "` `+` `str` `(res))` |

**Output :**

The original list is : [3, 5, 1, 6, 7, 9, 8, 5] The filtered list is : 9

**Method #2 : Using sum() + list comprehension**

This is different and elegant way to perform this particular task. It filters out all the numbers that are less than equal N and sums according to condition. This is one liner and preferred method to achieve this task.

`# Python 3 code to demonstrate ` `# Summation of first N matching condition` `# using sum() + list comprehension` ` ` `# initializing list` `test_list ` `=` `[` `3` `, ` `5` `, ` `1` `, ` `6` `, ` `7` `, ` `9` `, ` `8` `, ` `5` `]` ` ` `# printing original list` `print` `(` `"The original list is : "` `+` `str` `(test_list))` ` ` `# using sum() + list comprehension` `# to sum first N elements matching condition ` `# sum first 3 odd occurrences` `res ` `=` `sum` `([i ` `for` `i ` `in` `test_list ` `if` `i ` `%` `2` `!` `=` `0` `][:` `3` `])` ` ` `# printing result` `print` `(` `"The filtered list is : "` `+` `str` `(res))` |

**Output :**

The original list is : [3, 5, 1, 6, 7, 9, 8, 5] The filtered list is : 9

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