Reactive Sankey Diagram in R Shiny with multiple dataframes as input - r

Question

It's my first time creating a dashboard and I'm running into a problem I can't seem to solve. I have created a sankey diagram and I want to be able to interactively change its contents through different dataframes (in this example: level_1, level_2, level_3). I've only ever practiced this with a regular plot, where the input would come from a variable within one dataframe which is my starting point in this piece of code (e.g. I have a df$country, so I use input$country in my plot --> Then I could choose from different countries in the dashboard sidebar, in order to change the contents of the plot). I have no idea how to do this when the input has to come from seperate dataframes.
My code: (in app.R)
level_1 <- as.data.frame(matrix(sample(seq(0,40), 15, replace=T ), 3, 5))
level_2 <- as.data.frame(matrix(sample(seq(0,40), 20, replace=T ), 4, 5))
level_3 <- as.data.frame(matrix(sample(seq(0,40), 25, replace=T ), 5, 5))
levels <- list(level_1, level_2, level_3)
ui <- dashboardPage(
dashboardHeader(title = "title"),
dashboardSidebar(
selectInput("in_levels", "Levels", choices = levels)
),
dashboardBody(
fluidRow(sankeyNetworkOutput("widget1"))
)
)
server <- function(input, output) {
links <- input$in_levels %>%
rownames_to_column(var="source") %>%
gather(key="target", value="value", -1) %>%
filter(value != 0)
nodes <- data.frame(
name=c(as.character(links$source), as.character(links$target)) %>%
unique()
)
links$IDsource <- match(links$source, nodes$name)-1
links$IDtarget <- match(links$target, nodes$name)-1
output$widget1 <- renderSankeyNetwork({
sankeyNetwork(Links = links, Nodes = nodes,
Source = "IDsource", Target = "IDtarget",
Value = "value", NodeID = "name", fontSize = 14, nodeWidth = 60,
fontFamily = "Arial", iterations = 0, sinksRight=TRUE)
})
}
shinyApp(ui, server)
I thought maybe it would help to create a list(), levels, of all the dataframes, but that does not work. I get this error:
Error : Can't access reactive value 'in_levels' outside of reactive consumer.
i Do you need to wrap inside reactive() or observer()?
I've googled reactive() and observer() to try to find out what my next step should be, but I haven't found the solution yet. It would be much appreciated if someone could give me advice on how to proceed, changes to make or something to read to increase my understanding.
Thanks in advance!

Answer 1

If you want to access any input values in the server you need to use a reactive context. shiny won't allow you to do otherwise, but even if it did, if an input value is updated, the server-side code won't update to reflect the change. Since you want both links and nodes to be dynamic and both depend on each other, a neat solution might be to store both objects in a list as follows:
server <- function(input, output) {
plot_data <- reactive({
# Perform all your computation inside this reactive!
links <- input$in_levels %>%
rownames_to_column(var="source") %>%
gather(key="target", value="value", -1) %>%
filter(value != 0)
nodes <- data.frame(
name = c(as.character(links$source), as.character(links$target)) %>%
unique()
)
links$IDsource <- match(links$source, nodes$name)-1
links$IDtarget <- match(links$target, nodes$name)-1
# Return the data in a list
list(links = links, nodes = nodes)
})
# Access the datasets by calling the reactive and then treating as a normal list
output$widget1 <- renderSankeyNetwork({
sankeyNetwork(Links = plot_data()$links, Nodes = plot_data()$nodes,
Source = "IDsource", Target = "IDtarget",
Value = "value", NodeID = "name", fontSize = 14, nodeWidth = 60,
fontFamily = "Arial", iterations = 0, sinksRight=TRUE)
})
}
This is untested as my current version of R doesn't support the network3d package.
The concept of reactivity is tricky, but chapter 3 of Mastering Shiny should be very illuminating if you're new to shiny.