how to store the result of working on input (R, Shiny, reactive)

Question

I get input data from a file uploading widget ( reactive ) like:

Step 1 getData <- reactive(...) #psuedo code .

And I need to do some work on the data and somehow store the result:

Step 2 result #SOMEHOW# = Clean1(getData()) #psuedo code .

In the end I'll render the result like:

Step 3 output$DataAfter = renderTable({ result... }) #psuedo code .

How should I do Step 2 ? I tried result = reactive({ Clean1(getData()) }) , but there's an error: the input is class NULL before I upload the file.

---

The following code works , where I put the Clean1() function inside Step 1 getData()

ui.R

library(shiny)

shinyUI(fluidPage(
    titlePanel("Uploading Files"),

    sidebarLayout(

        sidebarPanel(

            fileInput('file1', 'Choose CSV File',
                      accept=c('text/csv', 
                               'text/comma-separated-values,text/plain', 
                               '.csv')),

            tags$hr()

        ),
        mainPanel(
            tableOutput('DataBefore'),
            tableOutput('DataAfter'),
            tableOutput('Aggregation')
        )
    )
))

server.R

library(shiny)

library(dplyr)
library(stringr)
library(stringdist)
library(qdapRegex)
source('Clean1.R')

shinyServer(function(input, output) {

    getData <- reactive({
        inFile <- input$file1
        if (is.null(inFile)) return(NULL)
        Clean1( read.csv(inFile$datapath) )

    })

    output$DataAfter = renderTable({
        as.data.frame( getData()[[1]] )

    })

    output$Aggregation = renderTable({
        as.data.frame( getData()[[2]] )

})

})

Clean1.R

Clean1 = function(data){

    data = data %>% sample_frac(1) 

    data = data %>%
        mutate_each(funs(toupper)) %>%    
        mutate_each(funs(gsub("[[:punct:]]", " ", .))) %>%
        mutate_each(funs(str_trim)) %>%
        mutate_each(funs(rm_white))

    by.town = data %>%
        group_by(State, Town) %>%
        summarise( Count = n() )

    return(list(data, by.town))
} 

---

Now I **store the result like: result = reactive({ Clean1(getData()) }) , and it shows error until I upload the file (still works in the end).

The error is

Don't know how to sample from objects of class NULL

This error should happen at the beginning of Clean1() . It seems to think getData() is NULL before I upload it.

ui. R and Clean1.R doesn't change.

server.R

library(shiny)

library(dplyr)
library(stringr)
library(stringdist)
library(qdapRegex)
source('Clean1.R')

shinyServer(function(input, output) {

    getData <- reactive({
        inFile <- input$file1
        if (is.null(inFile)) return(NULL)
        read.csv(inFile$datapath)

    })

    result = reactive({
        Clean1(getData())
    })

    output$DataAfter = renderTable({
        as.data.frame( result()[[1]] )

    })

    output$Aggregation = renderTable({
        as.data.frame( result()[[2]] )

})

})

So what's standard way to do Step 2 ? Let me know please. Thanks a lot!

Answer 1

The getData() is NULL when the code first evaluates, so that error makes sense. You could make the result a reactive value that is monitored by an observer, but I think that would be more work than necessary. If you want it to not display an error, try just wrapping the Clean1 in a tryCatch block that returns NULL on error.

result = reactive({
    tryCatch({
        Clean1(getData())
    }, error=function(e) NULL)
})