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
4 def initialize(records, columns: nil)
5 @records = records
6 @columns = columns || derive_columns(records)
7 end
8 
9 def to_csv
10 CSV.generate do |csv|
11 csv << @columns.map { |col| humanize(col) }
12 @records.each do |record|
13 csv << @columns.map { |col| format_value(record[col]) }
14 end
15 end
16 end
17 
18 def write(path)
19 File.write(path, to_csv)
20 end
21 
22 private
23 
24 def derive_columns(records)
25 records.flat_map(&:keys).uniq
26 end
27 
28 def humanize(key)
29 key.to_s.tr("_", " ").split.map(&:capitalize).join(" ")
30 end
31 
32 def format_value(value)
33 case value
34 when Time, DateTime then value.iso8601
35 when Date then value.strftime("%Y-%m-%d")
36 when Array then value.join("; ")
37 when nil then ""
38 else value.to_s
39 end
40 end
41end
01 / 01
STEP 01

Walkthrough

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

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