How to Write to a CSV Line by Line

How to write to a CSV line by line?

General way:

##text=List of strings to be written to file
with open('csvfile.csv','wb') as file:
    for line in text:
        file.write(line)
        file.write('\n')

OR

Using CSV writer :

import csv
with open(<path to output_csv>, "wb") as csv_file:
        writer = csv.writer(csv_file, delimiter=',')
        for line in data:
            writer.writerow(line)

OR

Simplest way:

f = open('csvfile.csv','w')
f.write('hi there\n') #Give your csv text here.
## Python will convert \n to os.linesep
f.close()

How to write a csv file line by line?

In this particular case (in other words, not in the most general sense), specifying the first element of List1 as the fillvalue argument when calling itertools.zip_longest() looks like it would make it work:

import csv, itertools

List1 = ['DealerName']
List2 = ['Person1','Person2']
List3 = ['crisp nori, hot rice, and cold fish', 'takeout,fancy presentation, piled']

with open("Output.csv", "w", newline="") as Output_File:
    Output_File.write("List1,List2,List3\n")
    writer = csv.writer(Output_File)
    rows = itertools.zip_longest(List1, List2, List3, fillvalue=List1[0])
    writer.writerows(rows)

Contents of output.csv file afterward:

List1,List2,List3
DealerName,Person1,"crisp nori, hot rice, and cold fish"
DealerName,Person2,"takeout,fancy presentation, piled"

Writing to a CSV file with only one header line

There are two issues with your code, the first is data is an list yet you're enclosing it in another list, i.e. [header] is the same as [['cost', 'tax', 'percentage_of_pay']] which is an list of lists.

Second you would normally write the header first then write the data in a loop one per data row

You probably want something like:

with open('Sales-and-cost.csv', 'w') as f:
    writer=csv.writer(f, delimiter='\t', lineterminator='\n')
    writer.writerow(header)
    
    for row in rows:
        writer.writerow(row)

Where rows is a list of lists containing the output data, i.e.

rows = [[price_1, taxes_1, pay_percentage_1],[price_2, taxes_2, pay_percentage_2],[price_3, taxes_3, pay_percentage_3]]

How to write a pandas dataframe to CSV file line by line, one line at a time?

If you really want to print line by line. (You should not).

for i in range(len(df)):
    df.loc[[i]].to_csv(output_csv_file,
        index=False,
        header=False,
        mode='a')

How to read a CSV file line by line and write to another CSV file. How to skip the first 4 rows while writing to another file using C#?

To Skip the first 4 lines of the input file you need to read a line on every iteration of the while loop

using (var writer = new StreamWriter(File.OpenWrite("D:\\work\\POCs\\POC_RESOURCES\\Pricing_Files\\index-edited-ap-east-1.csv")))
using (var reader = new StreamReader(File.OpenRead("D:\\work\\POCs\\SPOT_POC_RESOURCES\\Pricing_Files\\index-ap-east-1.csv")))
{
    var index = 0;
    while (!reader.EndOfStream)
    {
        var line = reader.ReadLine();
        if (index > 4)
        {
            Console.WriteLine(index);
            writer.WriteLine(line);
        }
        index++;
    }
}

Python CSV, How to append data at the end of a row whilst reading it line by line (row by row)?

Do backup your file before trying just in case.

You can write a new temporary file and move that into the place over the old file you read from.

from tempfile import NamedTemporaryFile
import shutil
import csv

filename = 'candidates.csv'
tempfile = NamedTemporaryFile('w', delete=False)

with open(filename, 'r', newline='') as csvFile, tempfile:
    writer = csv.writer(tempfile)

    for line in csvFile:
        csv_row = line.strip().split(',')
        csv_row.append(check_update(csv_row[7])) # this will add the data to the end of the list.
        writer.writerow(csv_row)

shutil.move(tempfile.name, filename)

R write list to CSV line by line

Rather than write serially, you can convert to a data.frame and just write all at once:

Generate fake data that looks similar to what you posted:

fakeVec <- function(dummy) t(setNames(rnorm(3), letters[1:3]))
my_list <- lapply(0:4, fakeVec)
names(my_list) <- 6000:6004

Here's the fake data:

$`6000`
              a          b         c
[1,] -0.2444195 -0.2189598 -1.442364

$`6001`
             a        b          c
[1,] 0.2742636 1.068294 -0.8335477

$`6002`
            a        b         c
[1,] -1.13298 1.927268 -2.123603

$`6003`
             a        b            c
[1,] 0.8260184 1.003259 -0.003590849

$`6004`
              a         b         c
[1,] -0.2025963 0.1192242 -1.121807

Then convert format:

# crush to flat matrix
my_mat <- do.call(rbind, my_list)
# add in list names as new column
my_df <- data.frame(id = names(my_list), my_mat)

Now you have a data.frame like this:

    id          a          b            c
1 6000 -0.2444195 -0.2189598 -1.442364429
2 6001  0.2742636  1.0682937 -0.833547659
3 6002 -1.1329796  1.9272681 -2.123603334
4 6003  0.8260184  1.0032591 -0.003590849
5 6004 -0.2025963  0.1192242 -1.121807439

Which you can just write straight to a file:

write.csv(my_df, 'my_file.csv', row.names=F)

How do I write to a CSV in Python, and have the new data below the last line?

The clue is you say you want to leave your CSV in a sorted state. To do that will involve first reading the whole file in. Adding your new information, sorting it based on the surname (and possibly then on the firstname). Finally writing the whole thing back.

I am assuming your file has a header. In which case you need to take care not to include that as part of the sort.

For example:

import csv

def append_list_as_row(file_name, row):
    filename = "MusicDatacopy.csv"

    # Read the existing file in
    with open(filename, newline='') as f_input:
        csv_reader = csv.reader(f_input)
        header = next(csv_reader)
        data = list(csv_reader)
        
    data.append(row)    # add the new row to the end
    data.sort(key=lambda x: (x[5], x[4]))    # sort the data based on s_name

    # Write the whole file back
    with open(filename, 'w', newline='') as f_output:
        csv_writer = csv.writer(f_output)
        csv_writer.writerow(header)
        csv_writer.writerows(data)

artist = input("Enter Artist name: ").title()
album = input("Enter Album name: ").title()
month = input("Enter month bought: ").title()
owner = input("Enter Name of Owner: ").title()
f_name = input("Enter artist f_name: ").title()
s_name = input("Enter artist s_name: ").title()
genre = input("Enter genre: ").title()

row_contents = [artist, album, month, owner, f_name, s_name, genre]
append_list_as_row('MusicDatacopy.csv', row_contents)

---

Related Topics