[Hogfather]

caty-zharr, рекомендую глянуть http://www.jstatsoft.org/article/view/v059i10

Tidy data is a standard way of mapping the meaning of a dataset to its structure. A dataset is
messy or tidy depending on how rows, columns and tables are matched up with observations,
variables and types. In tidy data:

1. Each variable forms a column.
2. Each observation forms a row.
3. Each type of observational unit forms a table.

This is Codd’s 3rd normal form (Codd 1990)