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 will always return an array of mode list.
If TRUE (the default), then if FUN always returns a
scalar, the tapply will return 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
.