collapse: groupid – R documentation

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groupid

Generate Run-Length Type Group-Id

Description

groupid is an enhanced version of data.table::rleid for atomic vectors. It generates a run-length type group-id where consecutive identical values are assigned the same integer. It is a generalization as it can be applied to unordered vectors, generate group id's starting from an arbitrary value, and skip missing values.

Usage

groupid(x, o = NULL, start = 1L, na.skip = FALSE, check.o = TRUE)

Arguments

`x`	an atomic vector of any type. Attributes are not considered.
`o`	an (optional) integer ordering vector specifying the order by which to pass through `x`.
`start`	integer. The starting value of the resulting group-id. Default is starting from 1. For C++ programmers, starting from 0 could be a better choice.
`na.skip`	logical. Skip missing values i.e. if `TRUE` something like `groupid(c("a", NA, "a"))` gives `c(1, NA, 1)` whereas `FALSE` gives `c(1, 2, 3)`.
`check.o`	logical. Programmers option: `FALSE` prevents checking that each element of `o` is in the range `[1, length(x)]`, it only checks the length of `o`. This gives some extra speed, but will terminate R if any element of `o` is too large or too small.

Value

An integer vector of class 'qG'. See qG.

Examples

groupid(airquality$Month)
groupid(airquality$Month, start = 0)
groupid(wlddev$country)[1:100]

## Same thing since country is alphabetically ordered: (groupid is faster..)
all.equal(groupid(wlddev$country), qG(wlddev$country, na.exclude = FALSE))

## When data is unordered, group-id can be generated through an ordering..
uo <- order(rnorm(fnrow(airquality)))
monthuo <- airquality$Month[uo]
o <- order(monthuo)
groupid(monthuo, o)
identical(groupid(monthuo, o)[o], unattrib(groupid(airquality$Month)))

collapse

Advanced and Fast Data Transformation

v1.5.3

GPL (>= 2) | file LICENSE

Authors

Sebastian Krantz [aut, cre], Matt Dowle [ctb], Arun Srinivasan [ctb], Laurent Berge [ctb], Dirk Eddelbuettel [ctb], Josh Pasek [ctb], Kevin Tappe [ctb], R Core Team and contributors worldwide [ctb], Martyn Plummer [cph], 1999-2016 The R Core Team [cph]

Initial release

2021-03-05