shiny/man/renderPrint.Rd

\name{renderPrint}
\alias{renderPrint}
\title{Printable Output}
\usage{
  renderPrint(expr, env = parent.frame(), quoted = FALSE,
    func = NULL)
}
\arguments{
  \item{expr}{An expression that may print output and/or
  return a printable R object.}

  \item{env}{The environment in which to evaluate
  \code{expr}.}

  \item{quoted}{Is \code{expr} a quoted expression (with
  \code{quote()})? This}

  \item{func}{A function that may print output and/or
  return a printable R object (deprecated; use \code{expr}
  instead).}
}
\description{
  Makes a reactive version of the given function that
  captures any printed output, and also captures its
  printable result (unless \code{\link{invisible}}), into a
  string. The resulting function is suitable for assigning
  to an \code{output} slot.
}
\details{
  The corresponding HTML output tag can be anything (though
  \code{pre} is recommended if you need a monospace font
  and whitespace preserved) and should have the CSS class
  name \code{shiny-text-output}.

  The result of executing \code{func} will be printed
  inside a \code{\link[utils]{capture.output}} call.

  Note that unlike most other Shiny output functions, if
  the given function returns \code{NULL} then \code{NULL}
  will actually be visible in the output. To display
  nothing, make your function return
  \code{\link{invisible}()}.
}
\examples{
isolate({

# renderPrint captures any print output, converts it to a string, and
# returns it
visFun <- renderPrint({ "foo" })
visFun()
# '[1] "foo"'

invisFun <- renderPrint({ invisible("foo") })
invisFun()
# ''

multiprintFun <- renderPrint({
  print("foo");
  "bar"
})
multiprintFun()
# '[1] "foo"\\n[1] "bar"'

nullFun <- renderPrint({ NULL })
nullFun()
# 'NULL'

invisNullFun <- renderPrint({ invisible(NULL) })
invisNullFun()
# ''

vecFun <- renderPrint({ 1:5 })
vecFun()
# '[1] 1 2 3 4 5'


# Contrast with renderText, which takes the value returned from the function
# and uses cat() to convert it to a string
visFun <- renderText({ "foo" })
visFun()
# 'foo'

invisFun <- renderText({ invisible("foo") })
invisFun()
# 'foo'

multiprintFun <- renderText({
  print("foo");
  "bar"
})
multiprintFun()
# 'bar'

nullFun <- renderText({ NULL })
nullFun()
# ''

invisNullFun <- renderText({ invisible(NULL) })
invisNullFun()
# ''

vecFun <- renderText({ 1:5 })
vecFun()
# '1 2 3 4 5'

})
}
\seealso{
  \code{\link{renderText}} for displaying the value
  returned from a function, instead of the printed output.
}