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# ------------------------------------------------------------------- |
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# ------------------ REACTIVES INSIDE FOR LOOPS --------------------- |
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# ------------------------------------------------------------------- |
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# ------------------------------------------------------------------- |
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# --- EXAMPLE 1: this works fine, because there are no reactives in - |
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# --- the for lopp -------------------------------------------------- |
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# ------------------------------------------------------------------- |
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library(shiny) |
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ui <- fluidPage( |
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verbatimTextOutput("txt") |
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) |
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server <- function(input, output, session) { |
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rv <- reactiveValues(one = 1, two = 2, three = 3) |
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output$txt <- renderPrint({ |
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vals <- list() |
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for (val in reactiveValuesToList(rv)) { |
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vals[[val]] <- val |
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} |
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for (i in seq_len(length(vals))) { |
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print(vals[[i]]) |
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} |
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}) |
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} |
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shinyApp(ui, server) |
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#> [1] 1 |
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#> [1] 2 |
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#> [1] 3 |
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# ------------------------------------------------------------------- |
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# --- EXAMPLE 2: this works fine, because even though there is a ---- |
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# --- reactive in the for lopp, it is invoked immediately (inside --- |
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# --- the for loop) ------------------------------------------------- |
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# ------------------------------------------------------------------- |
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library(shiny) |
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ui <- fluidPage( |
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verbatimTextOutput("txt") |
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) |
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server <- function(input, output, session) { |
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rv <- reactiveValues(one = 1, two = 2, three = 3) |
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output$txt <- renderPrint({ |
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vals <- list() |
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for (val in reactiveValuesToList(rv)) { |
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vals[[val]] <- reactive({ val })() |
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} |
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for (i in seq_len(length(vals))) { |
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print(vals[[i]]) |
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} |
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}) |
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} |
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shinyApp(ui, server) |
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#> [1] 1 |
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#> [1] 2 |
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#> [1] 3 |
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# ------------------------------------------------------------------- |
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# --- EXAMPLE 3: this does not work, because there is a reactive in - |
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# --- the for lopp that is only invoked outside the for loop -------- |
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# ------------------------------------------------------------------- |
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library(shiny) |
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ui <- fluidPage( |
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verbatimTextOutput("txt") |
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) |
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server <- function(input, output, session) { |
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rv <- reactiveValues(one = 1, two = 2, three = 3) |
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output$txt <- renderPrint({ |
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vals <- list() |
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for (val in reactiveValuesToList(rv)) { |
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vals[[val]] <- reactive({ val }) |
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} |
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for (i in seq_len(length(vals))) { |
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print(vals[[i]]()) |
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} |
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}) |
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} |
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shinyApp(ui, server) |
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#> [1] 3 |
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#> [1] 3 |
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#> [1] 3 |
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# --- Joe on this behavior: |
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# --- > It's because all the iterations of the for loop share the same |
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# --- > reference to el. So when any of the created reactive expressions |
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# --- > execute, they're using whatever the final value of el was. |
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# ------------------------------------------------------------------- |
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# --- EXAMPLE 4: this works, because even though there is a reactive |
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# --- in the for lopp that is only invoked outside of it, it is: ---- |
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# --- ---- |
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# --- * wrapped in a call to `local({ })`; ---- |
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# --- ---- |
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# --- * the iter variable (`val`) is assigned to `local({ })` ---- |
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# --- specific variable (`myVal`); ---- |
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# --- ---- |
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# --- * the super-assign operator (`<-`) is used ---- |
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# ------------------------------------------------------------------- |
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library(shiny) |
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ui <- fluidPage( |
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verbatimTextOutput("txt") |
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) |
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server <- function(input, output, session) { |
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rv <- reactiveValues(one = 1, two = 2, three = 3) |
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output$txt <- renderPrint({ |
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vals <- list() |
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for (val in reactiveValuesToList(rv)) { |
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local({ |
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myVal <- val |
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vals[[myVal]] <<- reactive({ myVal }) |
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}) |
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} |
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for (i in seq_len(length(vals))) { |
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print(vals[[i]]()) |
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} |
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}) |
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} |
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shinyApp(ui, server) |
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#> [1] 1 |
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#> [1] 2 |
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#> [1] 3 |
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# --- Joe on this behavior: |
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# --- > You can fix this by using a for loop but introducing a |
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# --- > local({...}) inside of there, and creating a local variable |
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# --- > in there whose value is assigned to el outside of the reactive. |
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# ------------------------------------------------------------------- |
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# --- EXAMPLE 5: this works, because we use lapply instead of a for - |
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# --- loop ---------------------------------------------------------- |
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# ------------------------------------------------------------------- |
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library(shiny) |
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ui <- fluidPage( |
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verbatimTextOutput("txt") |
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) |
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server <- function(input, output, session) { |
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rv <- reactiveValues(one = 1, two = 2, three = 3) |
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output$txt <- renderPrint({ |
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vals <- lapply( |
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reactiveValuesToList(rv), |
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function(x) { reactive(x) } |
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) |
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# --- Note that this alternative would not work because if doesn't |
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# --- get its own reference to the iter variable, so we always --- |
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# --- need to create a wrapper for the reactive ------------------ |
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# vals <- lapply( |
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# reactiveValuesToList(rv), |
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# reactive |
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# ) |
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for (i in seq_len(length(vals))) { |
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print(vals[[i]]()) |
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} |
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}) |
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} |
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shinyApp(ui, server) |
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#> [1] 1 |
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#> [1] 2 |
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#> [1] 3 |
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# --- Joe on this behavior: |
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# --- > You can fix this by using lapply instead of a for loop; since |
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# --- > each iteration executes as its own function call, it gets its |
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# --- > own reference to el. |
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bborgesr created this gist