r - Shiny with flexdashboard, dataframe as variable

Question

Using shiny within Flexdashboard I want to plot and display a dataframe where this dataframe is a variable from an input in my sidebar:

Inputs {.sidebar}
-----------------------------------------------------------------------

```{r}
selectInput("df", label = h3("Select df"),  choices = list("january" = "df1", "february" = "df2"))
```

I'm then plotting and displaying my dataframe inside a tabset:

Row {.tabset}
-----------------------------------------------------------------------

### Plot
```{r}
renderPlot({
plot(fread(paste("/Users/woshitom/Desktop/shiny/",input$df,".csv",sep="")),type="o", col="blue")
})
```

### Data
```{r}
renderTable(fread(paste("/Users/woshitom/Desktop/shiny/",input$df,".csv",sep="")))
```

As you can see I'm loading 2 times my csv:

fread(paste("/Users/woshitom/Desktop/shiny/",input$df,".csv",sep=""))

Instead I'd like to store it in a variable:

my_df <- fread(paste("/Users/woshitom/Desktop/shiny/",input$df,".csv",sep=""))

But when I do so I'm getting the following error:

Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

Any idea how i should store this dataframe?

Answer 1

Shiny inputs should be used inside render functions, observers or reactives. This is why you are getting the error. In your case since you want to store the result in a variable the way to go is to create a reactive variable with reactive(). This is the soltution:

my_df <- reactive({fread(paste("/Users/woshitom/Desktop/shiny/",input‌​$df,".csv",sep=""))}‌​)