Display error message when api call comes back empty in Shiny? - r

Question

I have an interactive visualization that connects to a city government's police data API.
When certain combinations of inputs are selected, my API call comes back empty and I get a nasty red error message (as my plot inputs are unavailable).
Can someone tell me how to display a more informative error message along the lines of, "there are no incidents matching your selection, please try again"? I would like this error message to appear as a showNotification and my ggplot not to render.
Below is an extremely stripped down version of what I am doing. Note how when a combination like "AVONDALE" and "CHEMICAL IRRITANT" is selected, the chart renders, whereas when a combination like "ENGLISH WOODS" and "TASER-BEANBAG-PEPPERBALL-40MM FOAM" is selected, an error message is returned. This error message is what I would like to address with a showNotification alert.
Note that this uses the Socrata API, so the package RSocrata must be installed and loaded.
install.packages("RSocrata")
library(shiny)
library(reshape2)
library(dplyr)
library(plotly)
library(shinythemes)
library(tibble)
library(RSocrata)
# Define UI for application that draws a histogram
ui <- fluidPage(
navbarPage("Example",
theme = shinytheme("united"),
tabPanel("Plot",
sidebarLayout(
sidebarPanel(
# neighborhood selector
selectizeInput("neighbSelect",
"Neighborhoods:",
choices = c("AVONDALE", "CLIFTON", "ENGLISH WOODS"),
multiple = FALSE)),
# incident description selector
selectizeInput("incSelect",
"Incident Type:",
choices = c("CHEMICAL IRRITANT", "TASER-BEANBAG-PEPPERBALL-40MM FOAM"),
multiple = FALSE))
),
# Output plot
mainPanel(
plotlyOutput("plot")
)
)
)
# Define server logic
server <- function(input, output) {
forceInput <- reactive({
forceInput <- read.socrata(paste0("https://data.cincinnati-oh.gov/resource/e2va-wsic.json?$where=sna_neighborhood= '", input$neighbSelect, "' AND incident_description= '", input$incSelect, "'"))
})
# Render plot
output$plot <- renderPlotly({
ggplot(data = forceInput(), aes(x = sna_neighborhood)) +
geom_histogram(stat = "count")
})
}
# Run the application
shinyApp(ui = ui, server = server)
Thank you so much for any help anyone can offer!

Answer 1

Im going to give an example with the shinyalert library to have the popup. Here I added the sample choice TEST to indicate no data:
#install.packages("RSocrata")
library(shiny)
library(reshape2)
library(dplyr)
library(plotly)
library(shinythemes)
library(tibble)
library(RSocrata)
library(shinyalert)
# Define UI for application that draws a histogram
ui <- fluidPage(
useShinyalert(),
navbarPage("Example",
theme = shinytheme("united"),
tabPanel("Plot",
sidebarLayout(
sidebarPanel(
# neighborhood selector
selectizeInput("neighbSelect",
"Neighborhoods:",
choices = c("AVONDALE", "CLIFTON", "ENGLISH WOODS","TEST"),
multiple = FALSE)),
# incident description selector
selectizeInput("incSelect",
"Incident Type:",
choices = c("CHEMICAL IRRITANT", "TASER-BEANBAG-PEPPERBALL-40MM FOAM"),
multiple = FALSE))
),
# Output plot
mainPanel(
plotlyOutput("plot")
)
)
)
# Define server logic
server <- function(input, output,session) {
forceInput <- reactive({
forceInput <- read.socrata(paste0("https://data.cincinnati-oh.gov/resource/e2va-wsic.json?$where=sna_neighborhood= '", input$neighbSelect, "' AND incident_description= '", input$incSelect, "'"))
if(nrow(forceInput)==0){
shinyalert("Oops!", "No data returned", type = "error")
forceInput <- NULL
}
forceInput
})
# Render plot
output$plot <- renderPlotly({
req(forceInput())
ggplot(data = forceInput(), aes(x = sna_neighborhood)) +
geom_histogram(stat = "count")
})
}
# Run the application
shinyApp(ui = ui, server = server)