Ruby CSV - 写在同一行而不覆盖？

Question

我正在使用

CSV.open(filename, "w") do |csv| 在一个 ruby​​.rb 文件中创建并写入 csv 文件，现在我需要打开它并在第二个 .rb 文件中对其进行编辑。现在我正在使用CSV.open(filename, "a") do |csv|，但这会创建新行而不是将新内容添加到现有行的末尾。

如果我第二次使用CSV.open(filename, "w") do |csv|，它会覆盖第一行。

编辑：

# Create export CSV
final_export_csv = "filepath_final.csv"

# Create filename for CSV file
imported_csv_filename = "imported_file.csv"

CSV.open(final_export_csv, "w", headers: ["several", "headers"] + [:new_header], write_headers: true) do |final_csv|

  # Read existing CSV file
  CSV.foreach(imported_csv_filename) do |old_csv_row|

    # Read a row, add the new column, write it to the new row
    CSV.open(denominator_csv_filename, "r+") do |new_csv_col|


# gathering some data code

          data = { passed.in }

          # Write data
     
          new_csv_col <<
          [
            passedin[:data]
          ]

          old_csv_row[:new_header] = passedin[:data]
          final_export_csv << old_csv_row

        end
      end
    end
  end
end

Answer 1

As tadman comments，您实际上无法就地编辑文件。好吧，您可以，但所有行都必须保持相同的长度。你没有这样做。

相反，读取一行，修改它，然后将其写入新的 CSV。然后用新文件替换旧文件。小心避免将整个 CSV 塞入内存，CSV 文件可能会变得非常大。

require 'csv'
require 'tempfile'
require 'fileutils'

csv_file = "test.csv"
# Write the new file to a tempfile to avoid polluting the directory.
temp = Tempfile.new

# Read the header line.
old_csv = CSV.open(csv_file, "r", headers: true, return_headers: true)
old_csv.readline

# Open the new CSV with the existing headers plus a new one.
new_csv = CSV.open(
  temp, "w",
  headers: old_csv.headers + [:new],
  write_headers: true
)

# Read a row, add the new column, write it to the new CSV.
old_csv.each do |row|
  row[:new] = 42
  new_csv << row
end

old_csv.close
new_csv.close

# Replace the old CSV with the new one.
FileUtils.move(temp.path, csv_file)