r shiny add element dynamically to reactive value

Question

I'm trying to learn how to use shiny modules to simplify a messy shiny app I have. The app currently reads in several data sets using a list of names like this:

dataSetsToLoad <- c("set1name", "set2name", "etc")
for (i in 1:length(dataSetsToLoad) {
dt <- readRDS(paste0(dataSetsToLoad[i], ".RDS")
assign(dataSetsToLoad[i], dt)
}

These end up in the global environment and are accessible to all my non-modularized code.

Following a code pattern from here, I'd like to modify the above to something like the following

stash = reactiveValues()
 for (i in 1:length(dataSetsToLoad) {
      stashVar <- paste0("stash$", dataSetsToLoad[i])
      dt <- readRDS(paste0(dataSetsToLoad[i], ".RDS")
      assign(stashVar, dt)
}

The summary question is how do I put the dt into the stash reactive with the dynamically created name in stashVar. A second question is whether there is any way to test this without actually running it in a shiny app.

save(df2, df1, file = "data.RData"). Did you know you can do something like this? You can easily save and load multiple data.frames in one RData File. — DSGym
– DSGym, Commented Jun 2, 2019 at 17:45
This is very useful! Thanks! But I don't see how it solves my problem of getting the data into stash. — JerryN
– JerryN, Commented Jun 2, 2019 at 18:49

DSGym · Accepted Answer · 2019-06-02 19:33:41Z

You can do something like this. Store the dataframes in a list and then assign them in a loop to the reactiveValues().

dflist <- list(mtcars, airquality, mtcars)

library(shiny)

# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 3,
                        value = 3)
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {

    values <- reactiveValues()

    for(i in 1:length(dflist)) {
        values[[paste0("df_", i)]] <- dflist[[i]]
    }

    observeEvent(input$bins, {
        print(values$df_1)
        print(values$df_2)
        print(values$df_3)
    })


}

# Run the application 
shinyApp(ui = ui, server = server)

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