Adding Date Filter to Flexdashboard

I would like the user to be able to select the date range of data they are interested in. This is my first time working with flexdashboard and Rshiny, so forgive if this is a simple question. I understand that user input requires you to use reactive expressions...

I tried searching stackoverflow for a while and still can't find an answer to help me. Here is the code I wrote so far.

---
title: "title"
output: 
  flexdashboard::flex_dashboard:
    orientation: rows
    vertical_layout: fill
    theme: lumen
    runtime: shiny
---

library(flexdashboard)
library(dplyr)
library(lubridate)
setwd("...")
data = readxl::read_excel("Resignation Data.xlsx")

Column {.sidebar}
-----------------------------------------------------------------------

Please choose the date range of interest.

```{r}
DateSeq = seq(as.Date("2020-07-13"), Sys.Date(), "day")
dateRangeInput("dateRange", "Date Select", format = "yyyy-mm-dd", start=min(DateSeq), end=max(DateSeq))

Row {data-width=150}
-----------------------------------------------------------------------

### ESS Utilization this month

```{r}
data_filter = renderTable({
    x = data[data$`Termination Date` >= input$dateRange[1] & data$`Termination Date` <= input$dateRange[2] | 
               is.na(data$`Termination Date`) & data$`Termination Initiation Date (HR)` >= input$dateRange[1] |
               is.na(data$`Termination Date`) & data$`Termination Initiation Date (ESS)` >= input$dateRange[1], ]
  })

renderGauge({
  utilization = round(length(which(!is.na(data_filter()$`Termination Initiation Date (ESS)`))) / length(data_filter()$`Employee ID`) * 100, 1)
  gauge(utilization, min = 0, max = 100, gaugeSectors(success = c(80, 100), warning = c(30, 79), danger = c(0, 29)))
  })

This results in a Warning: Error in $: $ operator is invalid for atomic vectors. And the gauge does not populate.

I am having trouble understanding how to access the filtered data in the reactive function. I tried using data_filter()$ based on this stackoverflow response Returning a dataframe in a reactive function in R Shiny Dashboard. Thank you for your help.

Solution

As @stefan already points out in the comments, you can only access the reactive data inside a reactive expression.

It seems that the problem is that utilization is still "reactive" but you use it in a non-reactive context when calling gauge.

Without seeing your whole dashboard and data, I would suggest to wrap gauge in a renderGauge call.

renderGauge({
  gauge(utilization, min = 0, max = 100, gaugeSectors(
    success = c(80, 100), warning = c(30, 79), danger = c(0, 29)))
})