groupid function

Generate Run-Length Type Group-Id

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.

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.

• 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.

Returns

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

See Also

seqid, timeid, qG, Fast Grouping and Ordering , Collapse Overview

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)))