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I have tried to make my program work, but as I don't have a lot of experience, I have faced a lot of problems. The idea of my work is that I analyze the data of the csv file and change the negative values to 0. So far I have managed to get all the data from the file and save it to a list, and manually assigning the "start" and "end" times of the file. 

import csv

data = []

filename = str(input("Give the file name: "))
    with open(filename) as csvfile:
        spamreader = csv.reader(csvfile, delimiter=';')
        for row in spamreader:
            data.append(row)

    print("File", filename, "is opened,", len(data),"rows will be analyzed.")

    data.pop(0) #deletes the header   

    print (f'Analyzing data between dates {data[0][0]} and {data[1097][0]}.') #data[row][column]

How is it possible to change the negative values in the data (screenshot) to 0, and then save everything to a new csv file? Help would be massivly appreciated. screenshot inside the CSV file asd

[In the actual data file there is 1000+ rows]

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  • I added the data file for download Commented Nov 17, 2018 at 21:52
  • 1
    As you start your question with "make my program work": is it pure coincidence that your screenshot and data file are the same as in stackoverflow.com/q/53325573/2564301 and "your work" bears more than a passing resemblance to my answer there? Commented Nov 17, 2018 at 21:57
  • We are friends. I didn't find it necessary to mention it, but we have divided the work so we get it made faster and we can teach each other. So I'm not copying anothers idea or code for no reason. Commented Nov 17, 2018 at 22:07

2 Answers 2

Reset to default
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If your file contains only numbers you can try the code below:

import csv
from collections import defaultdict

def convert(item):
    try:
        item = float(item)
        if item < 0:
            return 0
        else:
            return item
    except ValueError:
        return item

sums = defaultdict(list)

with open('Data.csv', 'r') as inp, open('output.csv', 'w', newline = '') as outp:
    reader = csv.reader(inp, delimiter = ';')
    writer = csv.writer(outp, delimiter = ';', dialect = 'excel')
    headers = next(reader)
    for line in reader:
        line = [convert(i) for i in line]
        sums[line[0]].append(line[1])
        writer.writerow(line)

for k,v in sums.items():
    print('key: {} total: {}'.format(k,sum(v)))

Firstly you can use the with context manager to open both files that you are going to read and write, from and to respectively. Then instead of storing it into a list, you can transform your data and directly write it to your target file, here named output.csv. The for line in reader here loops through the lines and transforms each value into an absolute integer before writing it to the file.

I added the defaultdict from the Python standard library if you want to store the values into a dictionary to use them. The dictionary sums will include a key by date and its values. To print the sum by days, you can simply use a string format to print the key and the summed values.

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10 Comments

The file not only integers
I added a helper function to check if it could be converted before turning it into an absolute value else it will just return the item as it is.
I don't really understand what your code does? The output (numers) are the same as in the input file, and there is extra spaces in between the cells.
Edited my answer based on your file, it was because of the delimiters and the newline settings for windows. Try and it and tell me what it is you do not understand.
That's perfect, thank you very much! If I'd want to sum all the values per day, how should it be done? So it would be 1.1.2016 369 416 2.1.2016 4 819 etc.. Would this be easy to do?
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0

This is very easily achieved using a pandas DataFrame:

import pandas as pd

c = pd.read_csv('inputcsvfile.csv')
processed_csv = c[c > 0].fillna(value=0)
processed_csv.to_csv('outputcsvfile.csv')

Pandas is an external library so you would need to install it (pip install pandas) before you can use this solution

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3 Comments

I have heard about panda, unfortunately this should be done in 'vanilla' python, so can't install external libraries.
Is this an assignment?
It's not an assignment, this is just to analyze a lot amount of data to use with my friends. So it would be best to use the existing libraries. Although I'm thinking of Pandas, as it makes life so much easier with data as you showed tour code

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