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.
|
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, and if the array would be one
dimensional the dimension is removed, to make it a vector.
|
...
|
optional arguments to FUN.
|
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), then
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. This is a vector if INDEX has only one
component.
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.
apply, lapply with its version
sapply.
groups <- as.factor(rbinom(32, n = 5, p = .4))
tapply(groups, groups, length) #- is almost the same as
table(groups)
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) #- does not yet print okay
tapply(1:n, fac, range) #- .. nor does this
tapply(1:n, fac, quantile) #- ... or this
ind <- list(c(1, 2, 2), c("A", "A", "B"))
table(ind)
tapply(1:3, ind) #-> the split vector
tapply(1:3, ind, sum)