tryCatch error handling doesn't work in shiny app? - r

Question

I'm doing some touch to my shiny app , the problem i'm encountering is that i can't handle the errors using tryCatch like :
tryCatch({
# expr
},
error = function(e) {
# handle the error
}
I'm using the Apriori algorithm within my application ,when the user choose a dataset ,he can also adjust the values of min-support and min-confidence, but sometimes with some values of these, apriori algorithm returns 0 rules , and the error occurs when trying to plot the graph of the association rules .
Here's a small spinet of my code so far :
Getting the file
...
...
...
Find the association rules :
rules <- reactive({
validate(
need(input$file, "Please choose a data set")
)
transactions = read.transactions(
file = file(input$file$datapath),
format = "basket",
sep = ","
)
minValue <- min(length(transactions),input$visualization)
rules <-
apriori(transactions[0:minValue],
parameter = list(
support = input$min_supp,
confidence = input$min_conf
))
print(length(transactions[0:minValue]))
return(rules)
})
Plot the obtained association rules :
output$graphChart <- renderPlot({
Sys.sleep(1)
validate(
need(input$file, "Please choose a data set")
)
set.seed(42)
# validate(
# need(length(rules()) == 0, "zero rules")
# )
tryCatch({
plot(rules(), method = "graph")
})
error = function(condition){
print('there was an error')
}
})
But nothing changed i still get the error and no message printed in the R studio's console
I tried this but it doesn't help me get rid of the error,
By the way i also get errors on other tabs when no rules found .
EDITED
As Pork mentioned in his comment ,i tried :
output$graphChart <- renderPlot({
Sys.sleep(1)
validate(
need(input$file, "Please choose a data set")
)
set.seed(42)
# validate(
# need(length(rules()) == 0, "zero rules")
# )
tryCatch({
plot(rules(), method = "graph",)
})
error=function(cond) {
message(cond)
return(NA)
}
warning=function(cond) {
message(cond)
# Choose a return value in case of warning
return(NULL)
}
})
And the error persist again,
Can someone help me please ?
Any suggestions or advice would be appreciated!
Thanks.

Answer 1

Here is a small example of how you may use tryCatch block. We shall use showNotification to notify the user of the error
library(shiny)
ui <- fluidPage(
sidebarPanel(width = 2,
selectInput("data","data",choices = c(1,2),selected = 1)
),
mainPanel(
plotOutput("graphChart")
)
)
server <- function(input, output, session) {
rules <- reactive({
if(input$data == 1){
return(mtcars$mpg)
}else{
"some error"
}
})
output$graphChart <- renderPlot({
tryCatch({
plot(rules())
}, warning = function(w) {
showNotification('there was a warning','',type = "error")
return()
}, error = function(e) {
showNotification('there was an error','',type = "error")
return()
}, silent=TRUE)
})
}
shinyApp(ui, server)