| tapply {base} | R Documentation |
Apply a function to each cell of a ragged array, that is to each (non-empty) group of values given by a unique combination of the levels of certain factors.
tapply(X, INDEX, FUN = NULL, ..., simplify = TRUE)
X |
an atomic object, typically a vector. |
INDEX |
list of factors, each of same length as X. |
FUN |
the function to be applied. In the case of functions like
+, %*%, etc., the function name must be quoted. If
FUN is NULL, tapply returns a vector which can be used
to subscript the multi-way array tapply normally produces. |
... |
optional arguments to FUN. |
simplify |
If FALSE, tapply always returns an array
of mode "list". If TRUE (the default), then if
FUN always returns a scalar, tapply returns an array
with the mode of the scalar. |
When FUN is present, tapply calls FUN for each
cell that has any data in it. If FUN returns a single atomic
value for each cell (e.g., functions mean or var) and
when simplify is TRUE, tapply returns a multi-way
array containing the values. The array has the same number of
dimensions as INDEX has components; the number of levels in a
dimension is the number of levels (nlevels()) in the
corresponding component of INDEX.
Note that contrary to S, simplify = TRUE always returns an
array, possibly 1-dimensional.
If FUN does not return a single atomic value, tapply
returns an array of mode list whose components are the
values of the individual calls to FUN, i.e., the result is a
list with a dim attribute.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
the convenience functions by and
aggregate (using tapply);
apply,
lapply with its versions
sapply and mapply.
require(stats)
groups <- as.factor(rbinom(32, n = 5, p = .4))
tapply(groups, groups, length) #- is almost the same as
table(groups)
data(warpbreaks)
## contingency table from data.frame : array with named dimnames
tapply(warpbreaks$breaks, warpbreaks[,-1], sum)
tapply(warpbreaks$breaks, warpbreaks[, 3, drop = FALSE], sum)
n <- 17; fac <- factor(rep(1:3, len = n), levels = 1:5)
table(fac)
tapply(1:n, fac, sum)
tapply(1:n, fac, sum, simplify = FALSE)
tapply(1:n, fac, range)
tapply(1:n, fac, quantile)
## example of ... argument: find quarterly means
data(presidents)
tapply(presidents, cycle(presidents), mean, na.rm = TRUE)
ind <- list(c(1, 2, 2), c("A", "A", "B"))
table(ind)
tapply(1:3, ind) #-> the split vector
tapply(1:3, ind, sum)