Inconsistent behavior during cell selection in DT datatable - r

Question

I have the shiny app below in which the user clicks on a cell in the upper table and the relative cell should be displayed in the lower table. The issue is that when I unselect the cells in the upper the cells in the lower not only remain but become more.
library(shiny)
library(DT)
data("mtcars")
ui <- shinyUI(
fluidRow(
DT::dataTableOutput("myDatatable"),
DT::dataTableOutput("myDatatable2")
)
)
server <- shinyServer(function(input, output, session) {
dat1 <- reactive({
matrix(iris[,5])
})
list_all <- reactiveVal(character())
observeEvent(input$myDatatable_cell_clicked, {
list_all(append(list_all(), input$myDatatable_cell_clicked$value))
})
output$myDatatable <- DT::renderDataTable(dat1(),
selection=list( target="cell"),
server = FALSE,
rownames=FALSE)
output$myDatatable2 <- DT::renderDataTable(matrix(list_all()),
selection="none",
server = FALSE,
rownames=FALSE)
})
shinyApp(ui, server)

Answer 1

Please try below:
library(shiny)
library(DT)
data("mtcars")
ui <- shinyUI(
fluidRow(
DT::dataTableOutput("myDatatable"),
DT::dataTableOutput("myDatatable2")
)
)
server <- shinyServer(function(input, output, session) {
dat1 <- reactive({
matrix(iris[,5])
})
list_all <- reactiveVal(character())
observeEvent(input$myDatatable_cells_selected, {
if (nrow(input$myDatatable_cells_selected) == 0) {
list_all(character())
} else {
list_all(dat1()[input$myDatatable_cells_selected[,1]])
}
})
output$myDatatable <- DT::renderDataTable(dat1(),
selection=list( target="cell"),
server = FALSE,
rownames=FALSE)
output$myDatatable2 <- DT::renderDataTable(matrix(list_all()),
selection="none",
server = FALSE,
rownames=FALSE)
})
shinyApp(ui, server)
The main difference is using input$myDatatable_cells_selected which keeps the currently selected cells as opposed to input$myDatatable_cell_clicked which contains the clicked cell even when unselected, causing your issue.

Answer 2

Here is another version based on input$myDatatable_cells_selected using reactive over reactiveVal (should always be the preferred way in shiny) + this works for multiple columns.
library(shiny)
library(DT)
library(datasets)
ui <- shinyUI(fluidRow(
DT::dataTableOutput("myDatatable"),
DT::dataTableOutput("myDatatable2")
))
server <- shinyServer(function(input, output, session) {
dat1 <- reactive({
data.frame(iris[, 5])
})
selected <- reactive({
req(input$myDatatable_cells_selected)
selected <- input$myDatatable_cells_selected
selected[, 2] <- selected[, 2] + 1
return(selected)
})
output$myDatatable <- DT::renderDataTable(
dat1(),
selection = list(target = "cell"),
server = FALSE,
rownames = FALSE
)
output$myDatatable2 <- DT::renderDataTable(
data.frame(dat1()[selected()]),
selection = "none",
server = FALSE,
rownames = FALSE)
})
shinyApp(ui, server)