How to Add a New Column to a CSV File Preserving Existing Values?

Adding a New Column to a CSV File

This article addresses the issue of adding a new column to multiple CSV files, existing in a format with two existing columns labeled "Name" and "Code." The desired output is to add a third column named "Berry" and populate its values with the "Name" values.

An initial Python script using the csv library attempted to append a 'Berry' value to each row, but encountered an error where only the new column was populated with 'Berry' values.

The Solution

The recommended code presented in the answer section provides a comprehensive solution:

• Read the first row from the input CSV file and append the header 'berry' to it.
• Iterate through the remaining lines and append the first value (the name) to each row.
• Write all modified rows to the output CSV file.

Implementation

Here's a revised and improved Python script based on the provided solution:

<code class="python">import csv

with open('input.csv', 'r') as infile, open('output.csv', 'w') as outfile:
    reader = csv.reader(infile)
    header = next(reader)
    header.append('Berry')
    writer = csv.writer(outfile)
    writer.writerow(header)

    for row in reader:
        row.append(row[0])
        writer.writerow(row)</code>

This script successfully appends the new "Berry" column to each row, populated with the corresponding "Name" values.

Additional Considerations

• Be aware that the default line terminator in Python's csv library is 'rn,' which may cause double spacing in output files. To specify a different line terminator, use the lineterminator parameter during CSV file writing.
• Consider using a list to store all the modified rows and write them in one operation with writerows. This approach can be more efficient for large files.

• The with statement can be used on multiple files in one line, as shown in the following example:

  <code class="python">with open('input.csv', 'r') as infile, open('output.csv', 'w') as outfile:
    # file operations</code>

The above is the detailed content of How to Add a New Column to a CSV File Preserving Existing Values?. For more information, please follow other related articles on the PHP Chinese website!