Reactive/Calculate column in dynamic Rhandsontable - r

Question

I am using rhandsonpackage and am using solution from below link from this to achieve following scenario - "The change of drop down should present user with a different set of input, that they further may modify, while some other columns continue recalculating"
R Shiny App: Reactive/Calculate column in Rhandsontable
It works perfectly when the initial DF(initialized as previous <- reactive({DF})) is static.
However if DF is dynamic and lets say different based on a dropdown selection, the logic doesn't work.
The core reason is that inside 'MyChanges' definition, even when this dynamic DF is updated, object keeps on working the old input$hotable1 (since the is.null(input$hotable1) condition is never met again). Hence although the dynamic DF is updated correctly in 'previous', it won't reflect in the 'MyChanges'. I tried setting a flag to capture when the dropdown changes and setting the input$hottable1 to NULL but it's a read only object and that operation errors out.
Here is the modified code snippet to reproduce the issue. Again, main issues is that at line 26, it ignores the updated 'previous()' object. Really appreciate any help with a resolution on this!
#rm(list = ls())
library(shiny)
library(rhandsontable)
library(shinyWidgets)
## Create the dataset
getdynamicDF <- function(selection){
if(selection=="a"){return(data.frame(num = 1:10, price = 1:10,Total = 1:10,stringsAsFactors = FALSE))}
else if (selection=="b"){return(data.frame(num = 11:20, price = 1:10,Total = 1:10,stringsAsFactors = FALSE))}
else if (selection=="c"){return(data.frame(num = 21:30, price = 1:10,Total = 1:10,stringsAsFactors = FALSE))}
}
# DF = data.frame(num = 1:10, price = 1:10,Total = 1:10,stringsAsFactors = FALSE)
numberofrows <- 10
server <- shinyServer(function(input, output, session) {
# Initiate your table
# dynamicDF <- function(option)
previous <- reactive({
getdynamicDF(input$mydropdown)
})
MyChanges <- reactive({
if(is.null(input$hotable1)){return(previous())}
else if(!identical(previous(),input$hotable1)){
# hot.to.df function will convert your updated table into the dataframe
mytable <- as.data.frame(hot_to_r(input$hotable1))
# here the second column is a function of the first and it will be multipled by 100 given the values in the first column
mytable <- mytable[1:numberofrows,]
# Add some test cases
mytable[,1][is.na(mytable[,1])] <- 1
mytable[,2][is.na(mytable[,2])] <- 1
mytable[,3] <- mytable[,1]*mytable[,2]
mytable
}
})
output$hotable1 <- renderRHandsontable({rhandsontable(MyChanges())})
})
ui <- basicPage(mainPanel(pickerInput(
inputId = "mydropdown",
label = "Option",
choices = c("a", "b", "c")
),
rHandsontableOutput("hotable1")))
shinyApp(ui, server)

Answer 1

Perhaps this is what you are looking for.
library(shiny)
library(rhandsontable)
library(shinyWidgets)
## Create the dataset
getdynamicDF <- function(selection){
if(selection=="a"){return(data.frame(num = 1:10, price = 1:10,Total = 1:10,stringsAsFactors = FALSE))}
else if (selection=="b"){return(data.frame(num = 11:20, price = 1:10,Total = 1:10,stringsAsFactors = FALSE))}
else if (selection=="c"){return(data.frame(num = 21:30, price = 1:10,Total = 1:10,stringsAsFactors = FALSE))}
}
#numberofrows <- 10
server <- shinyServer(function(input, output, session) {
new <- reactiveValues(dt=NULL)
previous <- eventReactive(input$mydropdown, {
req(input$mydropdown)
getdynamicDF(input$mydropdown)
})
observe({new$dt<-previous()})
observeEvent(input$hotable1, {
mytable <- as.data.frame(hot_to_r(input$hotable1))
mytable[,3] <- mytable[,1]*mytable[,2]
new$dt <- mytable
})
output$hotable1 <- renderRHandsontable({
rhandsontable(new$dt)
})
})
ui <- basicPage(mainPanel(pickerInput(
inputId = "mydropdown",
label = "Option",
choices = c("a", "b", "c")
),
rHandsontableOutput("hotable1")))
shinyApp(ui, server)