[R-Forge #1705] Change CJ internally not to expand, for efficiency

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#652 10 comentarios 0 reacciones 0 asignados Ver en GitHub

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Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
25/100
Tipo de issue
Refactorización
Claridad
Necesita aclaración
Estado de actividad
Estancado
Stack tecnológico
r
Área
data, performance

Línea de trabajo

Start by tracing CJ(), binarysearch, and [.data.table to understand how CJ columns are currently allocated and indexed. Review the linked R-Forge discussion and use datatable-help for the under-the-hood behavior; done means establishing and implementing a viable allocation-saving design without changing normal user-visible behavior.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

feature request

Submitted by: Matt Dowle; Assigned to: Nobody; R-Forge link

CJ() could return an irregular column length data.table (its inputs unchanged), marked somehow so that binarysearch knows to %% index through the CJ columns, rather than allocating long vectors and populating them as CJ currently does. Purely for speed, with no changes for users unless perhaps CJ() has been used outside [.data.table.

Or, more generally, data.table columns could be marked so that indexing to them knows they should be recycled, without actually allocating and recycling the columns. Discuss on datatable-help needed as under-the-hood code e.g. DT$foo[903] might not work if it was internally a short vector. In reality it's probably only useful for CJ() as regular data.table's only have recycled data perhaps to start with creating them with say an NA column but then are quickly populated. If a large table has a column with the same value (say NA or 0) for every row, perhaps the column is redundant. Can't imagine that recycling >1 items is often useful (other than in CJ()).

Lenguaje dominante
R
Estrellas
3.9k
Forks
1.1k
Merge medio
14 h 4 min
PR fusionados (30 d)
4

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