Reshape a table between wide and long form

Goal: Pivot a table from one-column-per-category (wide) to one-row-per-category (long), or back — the same reshape spreadsheet tools call “unpivot”/“pivot”.

Prerequisites: The table module, via -A or nodes.

Wide to long (pivot_longer)

Unpivot a set of columns into name/value row pairs, keeping the remaining columns as identifiers. value_columns is an array of column indices; names_to and values_to (both optional) name the two new columns.

$ mq -A 'import "table" | let t = first(table::tables()) | table::pivot_longer(t, [1, 2, 3], "quarter", "score")' README.md

Input:

| Name  | Q1 | Q2 | Q3 |
| ----- | -- | -- | -- |
| Alice | 10 | 20 | 30 |
| Bob   | 5  | 15 | 25 |

Output:

| Name  | quarter | score |
| ----- | ------- | ----- |
| Alice | Q1      | 10    |
| Alice | Q2      | 20    |
| Alice | Q3      | 30    |
| Bob   | Q1      | 5     |
| Bob   | Q2      | 15    |
| Bob   | Q3      | 25    |

Long to wide (pivot_wider)

The inverse: spread a key/value column pair back out into one column per distinct key, grouping rows by the remaining identifier columns. names_from is the column index whose distinct values become new headers; values_from supplies the values. Combinations missing from the input become empty cells.

$ mq -A 'import "table" | table::tables | first | table::pivot_wider(1, 2)' README.md

Feeding the long output above back in with pivot_wider(1, 2) reproduces the original wide table.

Notes

• pivot_longer and pivot_wider are exact inverses of each other for well-formed input, so use whichever direction matches the shape you’re starting from.
• No table::to_markdown call needed here — mq expands table objects to Markdown automatically in query output. See Extract all tables from a document for when to_markdown actually is required.