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plyr.Rd
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plyr.Rd
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\docType{package}
\name{plyr}
\alias{plyr}
\alias{plyr-package}
\title{plyr: the split-apply-combine paradigm for R.}
\description{
The plyr package is a set of clean and consistent tools
that implement the split-apply-combine pattern in R. This
is an extremely common pattern in data analysis: you
solve a complex problem by breaking it down into small
pieces, doing something to each piece and then combining
the results back together again.
}
\details{
The plyr functions are named according to what sort of
data structure they split up and what sort of data
structure they return:
\describe{ \item{a}{array} \item{l}{list}
\item{d}{data.frame} \item{m}{multiple inputs}
\item{r}{repeat multiple times} \item{_}{nothing} }
So \code{\link{ddply}} takes a data frame as input and
returns a data frame as output, and \code{\link{l_ply}}
takes a list as input and returns nothing as output.
}
\section{Row names}{
By design, no plyr function will preserve row names - in
general it is too hard to know what should be done with
them for many of the operations supported by plyr. If you
want to preserve row names, use \code{\link{name_rows}}
to convert them into an explicit column in your data
frame, perform the plyr operations, and then use
\code{\link{name_rows}} again to convert the column back
into row names.
}
\section{Helpers}{
Plyr also provides a set of helper functions for common
data analysis problems:
\itemize{ \item \code{\link{arrange}}: re-order the rows
of a data frame by specifying the columns to order by
\item \code{\link{mutate}}: add new columns or modifying
existing columns, like \code{\link{transform}}, but new
columns can refer to other columns that you just created.
\item \code{\link{summarise}}: like \code{\link{mutate}}
but create a new data frame, not preserving any columns
in the old data frame.
\item \code{\link{join}}: an adapation of
\code{\link{merge}} which is more similar to SQL, and has
a much faster implementation if you only want to find the
first match. \item \code{\link{match_df}}: a version of
\code{\link{join}} that instead of returning the two
tables combined together, only returns the rows in the
first table that match the second.
\item \code{\link{colwise}}: make any function work
colwise on a dataframe \item \code{\link{rename}}: easily
rename columns in a data frame \item
\code{\link{round_any}}: round a number to any degree of
precision \item \code{\link{count}}: quickly count unique
combinations and return return as a data frame. }
}