ruby 35 lines · 8 steps

Rendering an ASCII table in Ruby

Turn an array of row hashes into an aligned, bordered text table by measuring column widths first.

Explained by highlit

Intermediate text-formatting column-alignment recursion data-transformation

1def render_table(rows)
2  return "(no data)" if rows.empty?
3 
4  columns = rows.flat_map(&:keys).uniq
5  widths = columns.each_with_object({}) do |col, acc|
6    cell_lengths = rows.map { |row| stringify(row[col]).length }
7    acc[col] = [col.to_s.length, *cell_lengths].max
8  end
9 
10  separator = "+" + columns.map { |col| "-" * (widths[col] + 2) }.join("+") + "+"
11  header = format_row(columns.map { |col| [col, col.to_s] }, widths)
12 
13  lines = [separator, header, separator]
14  rows.each do |row|
15    cells = columns.map { |col| [col, stringify(row[col])] }
16    lines << format_row(cells, widths)
17  end
18  lines << separator
19 
20  lines.join("\n")
21end
22 
23def format_row(cells, widths)
24  padded = cells.map { |col, value| " #{value.ljust(widths[col])} " }
25  "|" + padded.join("|") + "|"
26end
27 
28def stringify(value)
29  case value
30  when nil then ""
31  when Hash then value.map { |k, v| "#{k}=#{stringify(v)}" }.join(", ")
32  when Array then value.map { |v| stringify(v) }.join(", ")
33  else value.to_s
34  end
35end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Measure every column's maximum width before drawing so all cells align consistently.
2Collecting keys across all rows lets you handle rows with differing shapes.
3A recursive stringifier gives you predictable cell text for nested values like hashes and arrays.

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