How to manipulate reactive expressions like a normal dataframe?

[YC]

Hi guys,

I'm quite new with using Shiny. The code below is actually part of an Rmarkdown file with Shiny coding in it.

I have an issue in handling reactive expressions within Shiny. Basically after calling a reactive expression, I can render or plot the expressions. What I cannot easily do is to manipulate that data after calling it.

I've managed to render and output load_table(). This just tells it to load the csv file on a button click. See code below:

```{r UI inputs}
wellPanel(
  fileInput("dataset", label = "Select a .csv File to upload",
            accept=c("text/csv",
                     "text/comma-separated-values,text/plain",
                     ".csv")),

actionButton(inputId = "loadbutton", label = "Load Data")
)

dataTableOutput("df")

```

```{r Server Functions}
load_table <- eventReactive(input$loadbutton, {
    # input$file1 will be NULL initially. After the user selects
    # and uploads a file, it will be a data frame with 'name',
    # 'size', 'type', and 'datapath' columns. The 'datapath'
    # column will contain the local filenames where the data can
    # be found.
    inFile <- input$dataset

    if (is.null(inFile)){
      return(NULL)}
    else {
      read.csv(inFile$datapath)}
    })

output$df <- renderDataTable({
  load_table()
})
```

However, once the user selects and loads the data - I can't seem to manipulate it because the reactive expressions doesn't work like a dataframe. What I want to do next is to create filters so my users can sift through load_table(). But R never seems to treat it like a normal table. And I can't get the table without using a reactive function.

I know there are solutions out there on StackExchange, and there are issues similar to mine but I can never get it to really work.


Zac

[Joe Cheng]

Write another reactive expression that reads load_table() and performs the various filtering operations on it, and returns the resulting data frame. For example, if input$columns had the names of the columns to show, you'd do

filtered <- reactive({

  df <- load_table()

  # Show only selected columns

  if (!is.null(input$columns)) {

    stopifnot(all(input$columns %in% names(df)))

    df <- df[,input$columns]

  }

  # apply other filters...

  df

})

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