Shiny not detecting input in output - r

Question

If I run the following code, everything runs fine:
library(dplyr)
library(tidyr)
library(shiny)
id <- 1:100
gender <- sample(c('M','F'), 100, replace=TRUE)
age <- sample(18:22, 100, replace=TRUE)
ethnicity <- sample(c('W','B','H','A','O'), 100, replace = TRUE)
grade <- sample(LETTERS[1:4], 100, replace=TRUE)
df <- cbind(id,gender,age,ethnicity,grade) %>% as.data.frame()
list1 <- list("id"="id","gender"="gender","age"="age","ethnicity"="ethnicity","grade"="grade")
list2 <- list("id"="id","gender"="gender","age"="age","ethnicity"="ethnicity","grade"="grade")
ui <-fluidPage(
selectInput("picker1", "PICKER 1", choices = list1, selected = "gender"),
selectInput("picker2", "PICKER 2", choices = list2, selected = "grade"),
tableOutput("crosstabs")
)
server <- function(input,output,session){
output$crosstabs <- renderTable({
t<-df %>% select_all() %>% select(-id) %>%
pivot_longer(cols = input$picker1) %>%
count(name,value, grade) %>% pivot_wider(names_from = grade, values_from = n)
t
})
}
shinyApp(ui,server)
But when I update output$crosstabs to include input$picker2, it returns an error. I'm rather confused, as I'm using the same structure, but simply with grade swapped out for input$picker2:
output$crosstabs <- renderTable({
t<-df %>% select_all() %>% select(-id) %>%
pivot_longer(cols = input$picker1) %>%
count(name,value, input$picker2) %>% pivot_wider(names_from = input$picker2, values_from = n)
t
})
What exactly is happening here?

Answer 1

It is a string and the count expects a unquoted column name, we can convert it to symbol and evaluate (!!)
server <- function(input,output,session){
output$crosstabs <- renderTable({
df %>%
select_all() %>%
select(-id) %>%
pivot_longer(cols = input$picker1) %>%
count(name,value, !!rlang::sym(input$picker2)) %>%
pivot_wider(names_from = input$picker2, values_from = n)
})
}
-testing