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% File src/library/stats/man/ave.Rd
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% File src/library/stats/man/ave.Rd
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% Part of the R package, https://www.R-project.org
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2007 R Core Team
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% Copyright 1995-2024 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{ave}
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\name{ave}
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\alias{ave}
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\title{Group Averages Over Level Combinations of Factors}
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\title{Group Averages Over Level Combinations of Factors}
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\description{
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  A function is applied to subsets of a vector \code{x}, where each
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  subset consists of those observations with the same factor levels.
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  The \code{\link{mean}} function is applied by default,
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  replacing the values in each group by the group \emph{ave}rage.
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}
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\usage{
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\usage{
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ave(x, \dots, FUN = mean)
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ave(x, \dots, FUN = mean)
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}
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}
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\alias{ave}
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\arguments{
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\arguments{
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  \item{x}{A numeric.}
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  \item{x}{a vector, typically numeric.}
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  \item{\dots}{Grouping variables, typically factors, all of the same
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  \item{\dots}{grouping variables, typically factors, all of the same
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    length as \code{x}. Groups are defined by the
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    \code{length} as \code{x}.}
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    \code{\link{interaction}} of these variables.}
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  \item{FUN}{Function to apply for each factor level combination.}
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  \item{FUN}{a function to apply for each factor level combination.
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}
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\description{
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  Subsets of \code{x[]} are averaged, where each subset consist of those
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  observations with the same factor levels.
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    (NOTE: If given, this argument must be named.)}
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}
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}
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\value{
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\value{
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  A numeric vector, say \code{y} of length \code{length(x)}.
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  A vector, say \code{y}, of the same length as \code{x}.
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  If grouping variables are missing, all elements of \code{y} are equal
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  If \code{\dots} is \code{g1, g2}, e.g.,
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  to \code{FUN(x)}. Otherwise, if, e.g., \code{\dots} is \code{g1, g2},
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  \code{y[i]} is equal to \code{FUN(x[j]}, for all \code{j} with
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  \code{y[i]} is equal to \code{FUN(x[sub])} with \code{sub} comprising all
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  \code{g1[j] == g1[i]} and \code{g2[j] == g2[i])}.
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  \code{j} for which \code{g1[j] == g1[i]} and \code{g2[j] == g2[i]}.
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}
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\seealso{
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  \code{\link{mean}}, \code{\link{split}}, \code{\link{tapply}}.
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}
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}
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\seealso{\code{\link{mean}}, \code{\link{median}}.}
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\examples{
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\examples{
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require(graphics)
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require(graphics)
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ave(1:3)  # no grouping -> grand mean
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ave(1:3)  # no grouping -> grand mean
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lines(ave(breaks, wool, tension              ), type = "s", col = "blue")
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lines(ave(breaks, wool, tension              ), type = "s", col = "blue")
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lines(ave(breaks, wool, tension, FUN = median), type = "s", col = "green")
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lines(ave(breaks, wool, tension, FUN = median), type = "s", col = "green")
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legend(40, 70, c("mean", "median"), lty = 1,
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legend(40, 70, c("mean", "median"), lty = 1,
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      col = c("blue","green"), bg = "gray90")
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      col = c("blue","green"), bg = "gray90")
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detach()
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detach()
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# Running index per group
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(g <- sample(c("u","s","e","R"), 24, replace = TRUE))
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ave(seq_along(g), g, FUN = seq_along)
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}
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}
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\keyword{univar}
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\keyword{univar}
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\keyword{category}