reactivity and rhandsontable - r

Question

I have recently discovered the rhandsontable package in r and it will be very useful in some of my r shiny projects. I have slightly modified what I saw here Get selected rows of Rhandsontable as a little tester for what I will use this package for.
I want to be able to let users change values of the data frame from within r using the rhandsontable package.So here I want df[1,1] to update each time I change that value. I am just a bit confused when it comes to wrapping a reactive function around render functions especially the renderRHandsontable function. I have used reactive functions with plotting but this is a bit different.
library(shiny)
library(rhandsontable)
ui=fluidPage(
rHandsontableOutput('table'),
verbatimTextOutput('selected'),
verbatimTextOutput("tr")
)
server=function(input,output,session)({
a<-c(1,2)
b<-c(3,4)
c<-rbind(df1,df2)
df1<-data.frame(df3)
#need reactive function around the following
output$table=renderRHandsontable(
rhandsontable(df1,selectCallback = TRUE,readOnly = FALSE)
)
output$selected=renderPrint({
cat('Selected Row:',input$table_select$select$r)
cat('\nSelected Column:',input$table_select$select$c)
cat('\nSelected Cell Value:',input$table_select$data[[input$table_select$select$r]][[input$table_select$select$c]])
df1[input$table_select$select$r,input$table_select$select$c]<-input$table_select$data[[input$table_select$select$r]][[input$table_select$select$c]]
})
#need reactive function around the following
output$tr <- renderText({
df1[1,1]
})
})
# end server
shinyApp(ui = ui, server = server)
It is an interesting area that will open up a lot in my shiny apps for users to play around with.
Thanks

Answer 1

Your code here is not reproducible. In the beginning of your server function, you used rbind() on df1 and df2when neither of these objects exist yet. R will throw an error (and it should!)
Because of that I will have to assume that your data frame is in fact the following:
a<-c(1,2)
b<-c(3,4)
c<-rbind(a,b)
df1<-data.frame(c)
To bind the reactivity output from Rhandsontable to your textOutput, you can use the observe() function from Shiny or even better, the handy hot_to_r function from rhandsontable itself. This function converts the handsontable data to R object.
Without changing your ui function, this will be your server function:
server <- function(input,output,session)({
a<-c(1,2)
b<-c(3,4)
c<-rbind(a,b)
df1<-data.frame(c)
output$table<-renderRHandsontable(
rhandsontable(df1)
)
#use hot_to_r to glue 'transform' the rhandsontable input into an R object
output$tr <- renderText({
hot_to_r(input$table)[1,1]
})
})
Then proceed to call your Shiny app as usual: shinyApp(ui = ui, server = server) and your output$tr now reacts to any edits on your table.