在一个闪亮的应用程序中，您如何明确引用来自 selectizeInput 的用户选择以读取特定的 csv 文件？

Question

I'm creating a Shiny app with a number of dropdowns using selectizeInput. One is called "Country" and has a list of countries, the other is called "Year" and has a list of years. The app will then populate a few charts based on the data for that country/year combination. I have one csv file in a folder for every country and every year, and putting all those files together as I have done creates a very slow app, so instead I would like to conditionally read into the server the specific country/year files based on those selections.

The Country input allows multiple selections (up to 5), the Year input only allows one.

All CSV files are formatted like this:

2014_UK.csv
2014_US.csv
2014_SA.csv
2015_UK.csv
2015_US.csv
....

What is the best way to do this?

Answer 1

One way to go about it is to create a reactive that reads in the data each time one of the inputs is changed.

# create some fake data
countries <- c('US', 'UK', 'SA')
years <- 2013:2015
x <- paste0(paste(rep(years, each = length(countries)), countries, sep = "_"), '.csv')
for (i in x){
  write.csv(data.frame(x=i, y=rnorm(5)), i)
}

library(shiny)
ui <- fluidPage(
  selectInput('year', 'year', years),
  selectInput('country', 'country', countries, multiple=T),  # multiple is T
  dataTableOutput('tbl', width='200px')
)
server <- function(input, output){
  r <- reactive({
    req(input$country)  # req country to be not NULL
    x <- paste0(input$year, '_', input$country, '.csv')  # paste inputs together, maybe more than 1
    l <- lapply(x, read.csv)  # read in all csvs in x
    do.call('rbind', l)  # bind them together
  })
  output$tbl <- renderDataTable(r())
}
shinyApp(ui, server)

In this app, each time one of the inputs is changed, the reactive block is executed and the output$tbl will render the new data.