In Python, with a list of extracted values from file, how to find sum of column of float values?

Question

I am having trouble find the sum of a column with a list of values that is extracted from a txt file using Python 3. The file contains data that looks something like:

• 1800 -0.19 -0.11
• 1801 -0.1 -0.17
• 1802 -0.2 -0.11
• .
• . [cont.]
• .
• 1900 -0.15 -.15

How can I find the sum of the second and third columns separately?

First, I opened the file using

with open('file.txt') as f:

for line in f:
    column_2 = line.split()
    b = float(column_2[-2])

    print(b)

I was able to print the second column of values successfully. However, after I added:

print(sum(b))

It was not able to run the code.

When I run the code, I am given the error:

'int' object is not callable

Answer 1

There are two things wrong with your code.

Firstly, you have assigned some value to sum. Do not use builtin names for your variables.

Execute del sum and everything will be fine.

However, your logic is still wrong because doing that only takes the sum of the last value of b. You need to store all values you have seen somewhere.

With the way you are doing things, the best method would be using an accumulator variable:

b_sum = 0

for line in f:
    column_2_value = float(line.split()[-2])
    b_sum += column_2_value 

A better approach, IMO, is to load the entire data structure into memory:

with open('Global_Temperature_Data_File.txt') as f:
    data = [row.split() for row in f.read().split('\n')]
    transposed_data = list(zip(*data))

This will turn transposed_data into a nested list, where each inner element represents one column.

You can then just do this:

b_sum = sum(transposed_data[2])