shiny (version 0.3.0)

reactivePrint: Printable Output

Description

Makes a reactive version of the given function that captures any printed output, and also captures its printable result (unless invisible), into a string. The resulting function is suitable for assigning to an output slot.

Usage

reactivePrint(func)

Arguments

func

A function that may print output and/or return a printable R object.

Details

The corresponding HTML output tag can be anything (though pre is recommended if you need a monospace font and whitespace preserved) and should have the CSS class name shiny-text-output.

The result of executing func will be printed inside a capture.output call.

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

See Also

reactiveText for displaying the value returned from a function, instead of the printed output.

Examples

isolate({

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

invisFun <- reactivePrint(function() invisible("foo"))
invisFun()
# ''

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

nullFun <- reactivePrint(function() NULL)
nullFun()
# 'NULL'

invisNullFun <- reactivePrint(function() invisible(NULL))
invisNullFun()
# ''

vecFun <- reactivePrint(function() 1:5)
vecFun()
# '[1] 1 2 3 4 5'


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

invisFun <- reactiveText(function() invisible("foo"))
invisFun()
# 'foo'

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

nullFun <- reactiveText(function() NULL)
nullFun()
# ''

invisNullFun <- reactiveText(function() invisible(NULL))
invisNullFun()
# ''

vecFun <- reactiveText(function() 1:5)
vecFun()
# '1 2 3 4 5'

})