The usual list of list, unlike conventional C type Matrix, can allow the nested list of lists with variable lengths, and when we require the summation of its columns, the uneven length of rows may lead to some elements in that element to be absent and if not handled correctly, may throw exception. Let’s discuss certain ways in which this problem can be performed in error-free manner.

**Method #1 : Using sum() + filter() + map() + list comprehension**

The combination of above three function combined with list comprehension can help us perform this particular task, the sum function helps to perform the summation, filter allows us to check for the present elements and all rows are combined using the map function. Works only with python 2

`# Python code to demonstrate ` `# Column summation in uneven sized lists` `# using sum() + filter() + map() + list comprehension` ` ` `# initializing list of lists` `test_list ` `=` `[[` `1` `, ` `5` `, ` `3` `], [` `4` `], [` `9` `, ` `8` `]]` ` ` `# printing original list ` `print` `(` `"The original list is : "` `+` `str` `(test_list))` ` ` `# using sum() + filter() + map() + list comprehension` `# Column summation in uneven sized lists` `res ` `=` `[` `sum` `(` `filter` `(` `None` `, j)) ` `for` `j ` `in` `map` `(` `None` `, ` `*` `test_list)]` ` ` `# printing result` `print` `(` `"The summation of columns is : "` `+` `str` `(res))` |

**Output :**

The original list is : [[1, 5, 3], [4], [9, 8]] The summation of columns is : [14, 13, 3]

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

If one desires not to play with the None values, one can opt for this method to resolve this particular problem. The zip_longest function helps to fill the not present column with 0 so that it does not has to handle the void of elements not present.

`# Python3 code to demonstrate ` `# Column summation in uneven sized lists` `# using list comprehension + sum() + zip_longest()` `import` `itertools` ` ` `# initializing list of lists` `test_list ` `=` `[[` `1` `, ` `5` `, ` `3` `], [` `4` `], [` `9` `, ` `8` `]]` ` ` `# printing original list ` `print` `(` `"The original list is : "` `+` `str` `(test_list))` ` ` `# using list comprehension + sum() + zip_longest()` `# Column summation in uneven sized lists` `res ` `=` `[` `sum` `(i) ` `for` `i ` `in` `itertools.zip_longest(` `*` `test_list, fillvalue ` `=` `0` `)]` ` ` `# printing result` `print` `(` `"The summation of columns is : "` `+` `str` `(res))` |

**Output :**

The original list is : [[1, 5, 3], [4], [9, 8]] The summation of columns is : [14, 13, 3]

Attention geek! Strengthen your foundations with the **Python Programming Foundation** Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the **Python DS** Course. And to begin with your Machine Learning Journey, join the **Machine Learning – Basic Level Course**