Return subsets of vectors, matrices or data frames which meet conditions.

1 2 3 4 5 6 7 8 9 10 |

`x` |
object to be subsetted. |

`subset` |
logical expression indicating elements or rows to keep: missing values are taken as false. |

`select` |
expression, indicating columns to select from a data frame. |

`drop` |
passed on to |

`...` |
further arguments to be passed to or from other methods. |

This is a generic function, with methods supplied for matrices, data frames and vectors (including lists). Packages and users can add further methods.

For ordinary vectors, the result is simply
`x[subset & !is.na(subset)]`

.

For data frames, the `subset`

argument works on the rows. Note
that `subset`

will be evaluated in the data frame, so columns can
be referred to (by name) as variables in the expression (see the examples).

The `select`

argument exists only for the methods for data frames
and matrices. It works by first replacing column names in the
selection expression with the corresponding column numbers in the data
frame and then using the resulting integer vector to index the
columns. This allows the use of the standard indexing conventions so
that for example ranges of columns can be specified easily, or single
columns can be dropped (see the examples).

The `drop`

argument is passed on to the indexing method for
matrices and data frames: note that the default for matrices is
different from that for indexing.

Factors may have empty levels after subsetting; unused levels are
not automatically removed. See `droplevels`

for a way to
drop all unused levels from a data frame.

An object similar to `x`

contain just the selected elements (for
a vector), rows and columns (for a matrix or data frame), and so on.

This is a convenience function intended for use interactively. For
programming it is better to use the standard subsetting functions like
`[`

, and in particular the non-standard evaluation of
argument `subset`

can have unanticipated consequences.

Peter Dalgaard and Brian Ripley

`[`

,
`transform`

`droplevels`

1 2 3 4 5 6 7 8 9 10 11 12 | ```
subset(airquality, Temp > 80, select = c(Ozone, Temp))
subset(airquality, Day == 1, select = -Temp)
subset(airquality, select = Ozone:Wind)
with(airquality, subset(Ozone, Temp > 80))
## sometimes requiring a logical 'subset' argument is a nuisance
nm <- rownames(state.x77)
start_with_M <- nm %in% grep("^M", nm, value = TRUE)
subset(state.x77, start_with_M, Illiteracy:Murder)
# but in recent versions of R this can simply be
subset(state.x77, grepl("^M", nm), Illiteracy:Murder)
``` |

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