How to make Shiny's input$var consumable for dplyr::summarise()

Question

I have the following Rmarkdown Shiny:

---
title: \"My Title\"
runtime: shiny
output: 
  flexdashboard::flex_dashboard:
    vertical_layout:          


        

Answer 1

Using the development version of dplyr (v0.5.0.9002) you could turn your string into a symbol using rlang::sym() and then use the unquote operator (!! or UQ) to refer to the variable in the dplyr verbs.

library(dplyr)

var1 <- "Good" # replace with input$op_id
var2 <- rlang::sym("price") # replace with input$col_id

diamonds %>%
  filter(cut == var1) %>%
  select_at(vars(!!var2)) %>%
  summarise_at(vars(!!var2), funs(mean, sd, n()))

Which gives:

## A tibble: 1 × 3
#      mean      sd     n
#     <dbl>   <dbl> <int>
#1 3928.864 3681.59  4906

---

Should you have more than one variable, use rlang::syms() with the unquote splice operator (!!! or UQS). For example:

var1 <- "Good" 
var2 <- rlang::syms(c("price", "depth")) 

diamonds %>%
  filter(cut == var1) %>%
  select_at(vars(UQS(var2))) %>%
  summarise_at(vars(UQS(var2)), funs(mean, sd, n()))

Which gives:

## A tibble: 1 × 6
#  price_mean depth_mean price_sd depth_sd price_n depth_n
#       <dbl>      <dbl>    <dbl>    <dbl>   <int>   <int>
#1   3928.864   62.36588  3681.59 2.169374    4906    4906

---

For more information, have a look at the quasiquotation section of the Programming with dplyr vignette