% Generated by roxygen2 (4.0.2): do not edit by hand
\name{group_by}
\alias{group_by}
\alias{group_by_}
\alias{regroup}
\title{Group a tbl by one or more variables.}
\usage{
group_by(.data, ..., add = FALSE)

group_by_(.data, ..., .dots, add = FALSE)
}
\arguments{
\item{.data}{a tbl}

\item{...}{variables to group by. All tbls accept variable names,
some will also accept functions of variables. Duplicated groups
will be silently dropped.}

\item{add}{By default, when \code{add = FALSE}, \code{group_by} will
override existing groups. To instead add to the existing groups,
use \code{add = TRUE}}

\item{.dots}{Used to work around non-standard evaluation. See
\code{vignette("nse")} for details.}
}
\description{
Most data operations are useful done on groups defined by variables in the
the dataset. The \code{group_by} function takes an existing tbl
and converts it into a grouped tbl where operations are performed
"by group".
}
\section{Tbl types}{


\code{group_by} is an S3 generic with methods for the three built-in
tbls. See the help for the corresponding classes and their manip
methods for more details:

\itemize{
  \item data.frame: \link{grouped_df}
  \item data.table: \link{grouped_dt}
  \item SQLite: \code{\link{src_sqlite}}
  \item PostgreSQL: \code{\link{src_postgres}}
  \item MySQL: \code{\link{src_mysql}}
}
}
\examples{
by_cyl <- group_by(mtcars, cyl)
summarise(by_cyl, mean(disp), mean(hp))
filter(by_cyl, disp == max(disp))

# summarise peels off a single layer of grouping
by_vs_am <- group_by(mtcars, vs, am)
by_vs <- summarise(by_vs_am, n = n())
by_vs
summarise(by_vs, n = sum(n))
# use ungroup() to remove if not wanted
summarise(ungroup(by_vs), n = sum(n))

# You can group by expressions: this is just short-hand for
# a mutate/rename followed by a simple group_by
group_by(mtcars, vsam = vs + am)
group_by(mtcars, vs2 = vs)

# You can also group by a constant, but it's not very useful
group_by(mtcars, "vs")

# By default, group_by sets groups. Use add = TRUE to add groups
groups(group_by(by_cyl, vs, am))
groups(group_by(by_cyl, vs, am, add = TRUE))

# Duplicate groups are silently dropped
groups(group_by(by_cyl, cyl, cyl))
}
\seealso{
\code{\link{ungroup}} for the inverse operation,
  \code{\link{groups}} for accessors that don't do special evaluation.
}