Reactive file reader — reactiveFileReader

v1.9.0|Source: R/reactives.R

Description

Given a file path and read function, returns a reactive data source for the contents of the file.

reactiveFileReader(intervalMillis, session, filePath, readFunc, ...)

Arguments

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.

session

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

filePath

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

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.

...

Any additional arguments to pass to 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).

Details

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 intervalMillis, filePath, and readFunc functions will each be executed in a reactive context; therefore, they may read reactive values and reactive expressions.

See also

reactivePoll()

Examples

if (FALSE) {
# Per-session reactive file reader
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, NULL, 'data.csv', read.csv)
function(input, output, session) {
  output$data <- renderTable({
    fileData()
  })
}
}