User-interactive table made from reactive data - r

Question

I am very new to Shiny and struggle to understand reactivity.
Context : I want user to choose a name for a column, add this column to a reactive table and then edit this table. The table is reactive (it comes from an uploaded file filtered by user).
Thanks to this answer everything work fine with a non-reactive table (see mydata <- mtcars[1:5,]).
But it doesn't work when mydata becomes reactive!
Here is a reproductible working example with NON-REACTIVE data from #dww answer:
library(rhandsontable)
ui <- fluidPage(
h2("The mtcars data"),
rHandsontableOutput("mytable"),
textInput('NewCol', 'Enter new column name'),
radioButtons("type", "Column type:",
c("Integer" = "integer",
"Floating point" = "numeric",
"Text" = "character")),
actionButton("goButton", "Update Table")
)
server <- function(input, output) {
mydata <- mtcars[1:5,]
output$mytable = renderRHandsontable(df())
df <- eventReactive(input$goButton, {
if(input$NewCol!="" && !is.null(input$NewCol) && input$goButton>0){
if (input$type == "integer") v1 <- integer(NROW(mydata))
if (input$type == "numeric") v1 <- numeric(NROW(mydata))
if (input$type == "character") v1 <- character(NROW(mydata))
newcol <- data.frame(v1)
names(newcol) <- input$NewCol
mydata <<- cbind(mydata, newcol)
}
rhandsontable(mydata, stretchH = "all")
}, ignoreNULL = FALSE)
observe(if (!is.null(input$mytable)) mydata <<- hot_to_r(input$mytable))
}
shinyApp(ui,server)
I have unsuccessfully tried these changes inside the code (basically I have changed all mydata for mydata()):
server <- function(input, output) {
# mydata <- reactive({ }) #make mydata a reactive object
output$mytable = renderRHandsontable(df())
df <- eventReactive(input$goButton, {
if(input$NewCol!="" && !is.null(input$NewCol) && input$goButton>0){
if (input$type == "integer") v1 <- integer(NROW(mydata()))
if (input$type == "numeric") v1 <- numeric(NROW(mydata()))
if (input$type == "character") v1 <- character(NROW(mydata()))
newcol <- data.frame(v1)
names(newcol) <- input$NewCol
mydata <<- cbind(mydata(), newcol)
}
rhandsontable(mydata(), stretchH = "all")
}, ignoreNULL = FALSE)
observe(if (!is.null(input$mytable)) mydata() <<- hot_to_r(input$mytable))}
I did not find this question answers/comments useful to answer my problem).
Could you explain how to use a reactive mydata inside #dww awesome answer?
[EDIT : title updated to better fit the answer]

Answer 1

I trimmed some extra features, like column data types... As a general rule - anything which you'd be rendering, can become reactive just by wrapping it in "reactive". Below I use "reactiveValues" but other reactive methods would work too.
A generalised way of making your output reactive to changes in the data's input -
foo_func = function() return(mydata)
foo_func_reactive = reactive(foo_func)
output$foo = renderMethod( foo_func_reactive() )
For your example:
shinyApp(
ui = fluidPage(
rHandsontableOutput("out_tbl"),
textInput(inputId = "in_txt", label = "New column name"),
actionButton(inputId = "in_btn1", label = "Add new column to the table above ..."),
actionButton(inputId = "in_btn2", label = "... Or, generate new data")
),
server = function(input, output, session) {
# establishes tbl_react as the holder for our reactive data, and pre-fills it for the first display with 1,2,3
tbl_react <- reactiveValues(tbl =
data.frame(a = c(1,2,3))
)
# button one adds a new column with the inputted name
observeEvent(input$in_btn1,{
newcolname <- as.character(input$in_txt)
newcol <- character(NROW(tbl_react$tbl))
tbl_react$tbl <- cbind(tbl_react$tbl, newcol)
colnames(tbl_react$tbl) <- c(colnames(tbl_react$tbl)[1:ncol(tbl_react$tbl)-1], newcolname)
})
# to show our output data is reactive, we can take a dependancy on button two to generate new data - this could instead be using an uploaded file
observeEvent(input$in_btn2,{
tbl_react$tbl <- data.frame(b = c(9,10,11))
})
output$out_tbl = renderRHandsontable( rhandsontable(tbl_react$tbl) )
}
)