Reason #112 • April 22nd, 2026

Array#transpose

Array#transpose turns columns into rows and rows into columns. It is a great way to destructure tabular data.

Ruby
rows = [
  ["Alice", "Ruby", "Stockholm"],
  ["Bob", "Rails", "Gothenburg"],
  ["Carol", "Hanami", "Malmo"]
]

names, favorite_frameworks, cities = rows.transpose

names
# => ["Alice", "Bob", "Carol"]
favorite_frameworks
# => ["Ruby", "Rails", "Hanami"]
cities
# => ["Stockholm", "Gothenburg", "Malmo"]
JavaScript
const rows = [
  ["Alice", "Ruby", "Stockholm"],
  ["Bob", "Rails", "Gothenburg"],
  ["Carol", "Hanami", "Malmo"],
];

const columns = rows[0].map((_, columnIndex) =>
  rows.map((row) => row[columnIndex])
);

const [names, favoriteFrameworks, cities] = columns;

console.log(names);
// => ["Alice", "Bob", "Carol"]
console.log(favoriteFrameworks);
// => ["Ruby", "Rails", "Hanami"]
console.log(cities);
// => ["Stockholm", "Gothenburg", "Malmo"]

Handy for transitioning between row-oriented and column-oriented data structures like database rows, CSV rows or matrices.

History

Array#transpose arrived in Ruby 1.8.0, released in 2003.

The name comes straight from linear algebra, where transposing a matrix swaps rows and columns.

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