How can I make data uploaded to a shiny app usable and then actually use it?

Question

I'm trying to build a shiny app and I've never done this before.

What I want to do is allow the user to upload data from a CSV file of the user's choice that looks something like this:

ID    Date        Name        Amount
123   01/12/2018  John Doe    100
124   01/02/2018  Bob Smith   110
125   01/03/2018  Jane Jones  100
126   01/02/2018  John Doe    110
127   01/03/2018  Bob Smith   100
128   01/04/2018  Jane Jones  110
129   01/03/2018  John Doe    100
130   01/04/2018  Bob Smith   110
131   01/04/2018  Jane Jones  120
132   01/14/2018  Tom Thomas  100

Then I want to have the app USE this data to run code such as this:

as.Date(myDF$Date, format="%m/%d/%Y")
sortedByDate = myDF[order(myDF$Date)]
amountPerDate = aggregate(data=myDF, Amount ~ Date, sum)
amountPerDate

to produce output such as this:

Date        Amount
01/02/2018  220
01/03/2018  300
01/04/2018  340
01/12/2018  100
01/14/2018  100

so the user can see the total amount per date, with the dates in correct order. I've been doing stuff like this in regular R script for months but have never before tried it in shiny.

So to upload the data into shiny I'm using this code:

shinyServer(function(input, output){
 output$contents <- renderTable({
  inFile <- input$file1
  if(is.null(inFile))
   return(NULL)
  userData = read.csv(inFile$datapath, sep=",")

  #here I run chunks of code to clean the data

  #assign data frame to global environment
  assign("userData", userData, envir = .GlobalEnv)

  #display data table in app
  userData
})

So now the user can look at the data but can't DO anything with it.

The data frame in the global environment has every variable as class Factor. I thought it would be easy to coerce the variables into their proper classes (Numeric for "ID" and "Amount", Character for "Name" and Date for "Date" but I can't do it. The very next thing I try to make the app do is display the date in the first row. I tried it with this code:

output$text <- renderText({
 userData$Date  = as.Date(as.character(userData$Date), format = "%m/%d/%Y")
 userData[1,2]
})

But the output in the app is 17533, NOT 01/12/2018 like I expected.

For some weird reason the following code WILL produce an output of 01/12/2018:

output$text <- renderText({
 userData$Date = as.character(userData$Date)
 userData[1,2]
})

but I need the dates to be class DATE, not class character.

Without the ability to coerce the variables into their proper classes my entire app is useless. Please help.

score 0 · Accepted Answer · answered Jan 13 '18 at 11:20

Don't use assign in Shiny, that is bad practice and it also doesn't allow for any reactivity. Instead, use a reactive to store your input data.

Regarding the unexpected printing output, this probably has to do with the way dates are stored. If you output a Date object in renderText, it will apparently parse it to it's integer value and convert that to character. To prevent that, parse it to character yourself first.

Here is a working example:

library(shiny)
library(data.table)
server <- function(input, output, session) {

  filedata <- reactive({
    infile <- input$file1
    if (is.null(infile)) {
      return(NULL)
    }
    df <- fread(infile$datapath)
    return(df)
  })

  output$my_table <- renderDataTable({
    if(is.null(filedata()))
    {
      return(NULL)
    }
    else
    {
      myDF <- filedata() # read the uploaded data from reactive
      myDF$Date <- as.Date(myDF$Date, format="%m/%d/%Y") # Change format!
      sortedByDate = myDF[order(myDF$Date)]
      amountPerDate = aggregate(data=myDF, Amount ~ Date, sum)
      print('done')
      return(amountPerDate)
    }
  })

  output$my_text <- renderText({
    if(is.null(filedata()))
    {
      return(NULL)
    }
    else
    {
      as.character(as.Date(filedata()$Date, format="%m/%d/%Y"))[1]
    }
  })
}


ui <- fluidPage(
  fileInput("file1", "Choose CSV File",
            accept = c(
              "text/csv",
              "text/comma-separated-values,text/plain",
              ".csv")
  ),
  dataTableOutput('my_table'),
  textOutput('my_text')
)

shinyApp(ui,server)

Hope this helps!

How can I make data uploaded to a shiny app usable and then actually use it?

1 Answers1