


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>
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