How to delete element from reactiveValues in shiny? - r

Question

How to delete element from reactiveValues()
For example, when I run the code:
library(shiny)
runApp(list(
ui=tableOutput("table1"),
server=function(input, output, session) {
values <- reactiveValues(val1 = 1, val2 =2, val3 = 3)
values$val1 <- NULL
output$table1 <- renderPrint(reactiveValuesToList( values) )
}))
The output is:
$val1 NULL $val2 [1] 2 $val3 [1] 3
Instead of:
$val2 [1] 2 $val3 [1] 3
Thank you!

Answer 1

If you still want to use the assignment to NULL to remove values, you can assign the reactive value to be a list. See below for a simple modification to Zygmunt Zawadzki's answer. Then operate on the list in the usual R way to reflect the changes in your data.
library(shiny)
ui <- fluidPage(
mainPanel(
actionButton("delete", "delete"),
verbatimTextOutput("table1")
)
)
)
runApp(list(
ui=ui,
server=function(input, output, session) {
values <- reactiveValues(data=list(val1 = rnorm(1e7), val2 =2, val3 = 3))
observeEvent(input$delete,{
values$data$val1 <- NULL
})
output$table1 <- renderPrint({
res <- capture.output(gc())
cat(res, sep = "\n")
# No reactiveValuesToList needed
# x <- reactiveValuesToList(values)
length(values$data)
})
}))

Answer 2

I'll try to addres this:
I would like to delete elements from a reactiveValues object because I am using it to store user-defined list objects that can be quite large individually. My concern is that if the user creates too many such objects in a single session it will cause the app to crash due to insufficient memory.
When you assign NULL to the value R will remove the element from memory. See the app below - when you click delete button the memory is released:
library(shiny)
ui <- fluidPage(
mainPanel(
actionButton("delete", "delete"),
verbatimTextOutput("table1")
)
)
)
runApp(list(
ui=ui,
server=function(input, output, session) {
values <- reactiveValues(val1 = rnorm(1e7), val2 =2, val3 = 3)
observeEvent(input$delete,{
values$val1 <- NULL
})
output$table1 <- renderPrint({
res <- capture.output(gc())
cat(res, sep = "\n")
x <- reactiveValuesToList(values)
length(x)
})
}))
The two images below show you the state before clicking the delete, and after -> note that the value used by R has changed.
Those missing 80mb is the size of the val1 vector.
pryr::object_size(rnorm(1e7))
# 80 MB