Clean datatable when new data are loaded - r

Question

I'd like to load a table from a file, make some computations (ie. sum elements of two columns) when I click a button and show the results into a datatable. Easy. However, every time I load a new file, I'd like to clean the previous results and not show them, otherwise, it is confusing whether they are the results of the new or the old ones.
Here's what I tried. but I didn't succeeed on it...
example table: tab.csv
x;A;B
x1;1;0
x2;2;1
x3;1;1
x4;5;2
x5;3;3
code: ui.R
shinyUI(pageWithSidebar(
headerPanel(""),
sidebarPanel(),
mainPanel(fluidRow(
fileInput("table", "Choose CSV File"),
actionButton("BUTCS", "Compute sum"),
dataTableOutput("tablesum")
))
))
server.R
shinyServer(function(input, output) {
user <- new.env()
user$table <- NULL
user$tablesum <- NULL
observe({
if(is.null(input$table)){return()}
tablefilecsv <- input$table
user$table <- read.csv2(tablefilecsv$name, header = TRUE)
})
observeEvent(input$table, {
if(is.null(input$table)){return()}
user$tablesum <- NULL
})
output$tablesum <- renderDataTable(
{
if(is.null(input$BUTCS)){return()}
d <- user$table
user$tablesum <- data.frame(x=d$x, sum=(d$A+d$B))
}, options = list(paging = FALSE,searching = FALSE))
})

Answer 1

Try, i think it is what you want
shinyServer(function(input, output) {
user <- reactiveValues(table= NULL, tablesum= NULL)
observeEvent(input$table, {
if(is.null(input$table)){
return()
}else{
tablefilecsv <- input$table
user$table <- read.csv2(tablefilecsv$datapath ,header = TRUE)
output$tablesum <- renderDataTable(NULL)
}
})
observeEvent(input$BUTCS,{
output$tablesum <- renderDataTable({
d <- user$table
user$tablesum <- data.frame(x=d$x, sum=(d$A+d$B))
}, options = list(paging = FALSE,searching = FALSE))
})
})
Option using reactive functional ( added by #Stefano)
shinyServer(function(input, output) {
data <- reactive({
tablefilecsv <- input$table
table <- read.csv2(tablefilecsv$name, header=TRUE)
})
observeEvent(input$table,{
output$tablesum <- renderDataTable(NULL)
})
observeEvent(input$BUTCS,{
output$tablesum <- renderDataTable({
d <- data()
tablesum <- cbind.data.frame(x=d$x, sum=(d$A+d$B))
}, options = list(paging=FALSE, searching=FALSE))
})
})