How to extract only the a specific column of a CSV file in python

Question

We have to compute the average of of the 5th row in an excel sheet, saved as a csv file. The first row of the file has the names of the columns making them strings. I can't seem to get a code that loops around all the row[4] and compute it into one variable 'sum'. Here is my code. Also,

import csv
import os
sum = x_length = 0
with open('2.5_week.csv', newline='') as f:
    rows = csv.reader(f)
    for row in rows:
        if row[4] is int:
            sum = sum + float(row[4])
            x_length = x_length + 1
x_average = sum/len(x_length)
print(x_average)

I'm using python 3.4.x

Noctis Skytower · Accepted Answer · 2015-10-22 17:37:23Z

This example should help get you towards the goal you are trying to solve with your program:

import csv
import random
import statistics


def main():
    make_csv()
    read_csv_1()
    read_csv_2()


def make_csv():
    with open('2.5_week.csv', 'w', newline='') as file:
        writer = csv.writer(file)
        for index in range(1000):
            row = (random.random() * index,
                   random.randint(index, index * 2),
                   random.randrange(1 + index * 3),
                   random.random() + index,
                   random.randint(index, index + 10),
                   random.randrange(1 + index ** 2))
            writer.writerow(row)


def read_csv_1():
    with open('2.5_week.csv', 'r', newline='') as file:
        table = pivot_table(csv.reader(file))
    print(statistics.mean(map(float, table[4])))


def pivot_table(table):
    iterator = iter(table)
    pivot = tuple([cell] for cell in next(iterator))
    for row in iterator:
        for column, cell in zip(pivot, row):
            column.append(cell)
    return pivot


def read_csv_2():
    with open('2.5_week.csv', 'r', newline='') as file:
        print(statistics.mean(float(row[4]) for row in csv.reader(file)))

if __name__ == '__main__':
    main()

LetzerWille · Accepted Answer · 2015-10-22 17:35:42Z

0

total = 0
count = 0

with open("data.csv") as source:
    rdr = csv.reader(source, delimiter=',')
    next(rdr, None) #skip the header
    for row in rdr:
        try:
            if isinstance(float(row[4]),float):
                total+= float(row[4])
                count += 1
        except ValueError:
            pass

ave = round(total / count,2)
print(ave)

edited Oct 22, 2015 at 17:35

answered Oct 22, 2015 at 16:36

LetzerWille

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4 Comments

Jessy White Over a year ago

It keeps saying 'mag' which is the name of the column, can not be converted from string to float

LetzerWille Over a year ago

@JessyWhite if can skip the header with next(rows, None), just after you start the reader, I will update now.

LetzerWille Over a year ago

@JessyWhite I have update once again to make more robust

Noctis Skytower Over a year ago

@LetzerWille How do you find out who voted which way? I did not vote but have sometimes wondered who has contributed to the score of a question or answer.

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