ruby 41 lines · 7 steps

Turning records into CSV in Ruby

A small class that renders a list of hashes into CSV with derived headers and typed value formatting.

Explained by highlit

Intermediate csv data-export serialization pattern-matching encapsulation

1require "csv"
2 
3class CsvExporter
def initialize(records, columns: nil)
  @records = records
  @columns = columns || derive_columns(records)
end
8 
def to_csv
  CSV.generate do |csv|
    csv << @columns.map { |col| humanize(col) }
    @records.each do |record|
      csv << @columns.map { |col| format_value(record[col]) }
    end
  end
end
17 
def write(path)
  File.write(path, to_csv)
end
21 
private
23 
def derive_columns(records)
  records.flat_map(&:keys).uniq
end
27 
def humanize(key)
  key.to_s.tr("_", " ").split.map(&:capitalize).join(" ")
end
31 
def format_value(value)
  case value
  when Time, DateTime then value.iso8601
  when Date then value.strftime("%Y-%m-%d")
  when Array then value.join("; ")
  when nil then ""
  else value.to_s
  end
end
41end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Deriving columns from the data lets an exporter handle records with varying keys without hard-coded configuration.
2Centralizing value formatting in one method keeps every cell consistently serialized regardless of type.
3CSV.generate builds a string incrementally, so the same logic serves both in-memory output and file writing.

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