shiny/man/reactiveFileReader.Rd

\name{reactiveFileReader}
\alias{reactiveFileReader}
\title{Reactive file reader}
\usage{
  reactiveFileReader(intervalMillis, session, filePath,
    readFunc, ...)
}
\arguments{
  \item{intervalMillis}{Approximate number of milliseconds
  to wait between checks of the file's last modified time.
  This can be a numeric value, or a function that returns a
  numeric value.}

  \item{session}{The user session to associate this file
  reader with, or \code{NULL} if none. If non-null, the
  reader will automatically stop when the session ends.}

  \item{filePath}{The file path to poll against and to pass
  to \code{readFunc}.  This can either be a single-element
  character vector, or a function that returns one.}

  \item{readFunc}{The function to use to read the file;
  must expect the first argument to be the file path to
  read. The return value of this function is used as the
  value of the reactive file reader.}

  \item{...}{Any additional arguments to pass to
  \code{readFunc} whenever it is invoked.}
}
\value{
  A reactive expression that returns the contents of the
  file, and automatically invalidates when the file changes
  on disk (as determined by last modified time).
}
\description{
  Given a file path and read function, returns a reactive
  data source for the contents of the file.
}
\details{
  \code{reactiveFileReader} works by periodically checking
  the file's last modified time; if it has changed, then
  the file is re-read and any reactive dependents are
  invalidated.

  The \code{intervalMillis}, \code{filePath}, and
  \code{readFunc} functions will each be executed in a
  reactive context; therefore, they may read reactive
  values and reactive expressions.
}
\examples{
\dontrun{
# Per-session reactive file reader
shinyServer(function(input, output, session)) {
  fileData <- reactiveFileReader(1000, session, 'data.csv', read.csv)

  output$data <- renderTable({
    fileData()
  })
}

# Cross-session reactive file reader. In this example, all sessions share
# the same reader, so read.csv only gets executed once no matter how many
# user sessions are connected.
fileData <- reactiveFileReader(1000, session, 'data.csv', read.csv)
shinyServer(function(input, output, session)) {
  output$data <- renderTable({
    fileData()
  })
}
}
}
\seealso{
  \code{\link{reactivePoll}}
}