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tapply(X, INDEX, FUN = NULL, ..., simplify = TRUE)X. The elements are coerced to factors by as.factor.NULL. In the case of
functions like +, %*%, etc., the function name must
be backquoted or quoted. If FUN is NULL, tapply
returns a vector which can be used to subscript the multi-way array
tapply normally produces.FUN: the Note section.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.FUN is not NULL, it is passed to
match.fun, and hence it can be a function or a symbol or
character string naming a function.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 such cell (e.g., functions mean or var)
and when simplify is TRUE, tapply returns a
multi-way array containing the values, and NA for the
empty cells. 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 if the return value has a class (e.g., an
object of class "Date") the class is discarded.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.When there is an array answer, its dimnames are named by
the names of INDEX and are based on the levels of the grouping
factors (possibly after coercion).For a list result, the elements corresponding to empty cells are
NULL.
by and
aggregate (using tapply);
apply,
lapply with its versions
sapply and mapply.
require(stats)
groups <- as.factor(rbinom(32, n = 5, prob = 0.4))
tapply(groups, groups, length) #- is almost the same as
table(groups)
## 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, length = 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
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)
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