Group By Nest in Shiny

[jdurvesh]

Hi Friends ,
Can you please help to correct the errors in below code as im unable to use group_by and nest in shiny. Below is simplified example.

library(tidyverse)
library(shiny)

x<-rnorm(10,100,20)
y<-c("a","a","a","a","a","b","b","b","b","b")
t<-data.frame(x,y)

ui<-fluidPage(
  
  mainPanel(
    selectInput("Grp","Input Group",choices=names(t)),
    tableOutput("table_1")
  )
)

Fraction<-function(df){
  df/sum(df)
}
server <-function(input,output){
     nested<-reactive({
    req(input$Grp)
    t %>%
       group_by(input$Grp)%>%
      nest()
     })
   
  output$table_1<-renderTable({
    map(nested()$data,Fraction)
  })
  
  }
shinyApp(ui=ui,server=server)
'''

----------------------
The normal R code works fine  that is similar to above 
x <- rnorm(10, 100, 20)
y <- c("a", "a", "a", "a", "a", "b", "b", "b", "b", "b")
t <- data.frame(x, y)
t1 <- t %>% group_by(y) %>% nest()
Fraction <- function(df) {
  df / sum(df)
}
t2 <- map(t1$data, Fraction)
t2

[nirgrahamuk]

@jdurvesh

x <- rnorm(10, 100, 20)
y <- c("a", "a", "a", "a", "a", "b", "b", "b", "b", "b")
t <- data.frame(x, y)
t1 <- t %>% group_by(y) %>% nest()
Fraction <- function(df) {
  df / sum(df)
}
t2 <- map(t1$data, Fraction)
t2

in your working code, group_by(y) works where y is the symbol for the name to group on, but in your shiny app input$Grp is itself a symbol (one not present in your t df.
the value of input$Grp might be "y" , to 'get at it' use library(rlang)

 t %>%
       group_by(!!sym(input$Grp))%>%
      nest()

[jdurvesh]

Hi Sir ,
Thanks for prompt help any resources u can recommend where such differences between R and Shiny can be found.

[nirgrahamuk]

Its not really a difference.
input$Grp is like any variable in base R as far as the group by is concerned

in base R without shiny if you had

x <- rnorm(10, 100, 20)
y <- c("a", "a", "a", "a", "a", "b", "b", "b", "b", "b")
t <- data.frame(x, y)
variable_to_group_by <- "y"

#would fail
t1 <- t %>% group_by(variable_to_group_by ) %>% nest()
#would work
t1 <- t %>% group_by(!!sym(variable_to_group_by )) %>% nest()

[GreyMerchant]

You can have a look here at shiny specifically: https://mastering-shiny.org/
and then on the !! (bang bang operator) you can have a look here: https://adv-r.hadley.nz/meta-big-picture.html this relates to normal R but can be used in shiny as @nirgrahamuk showed.

[smichal]

Here, you are briefly touching the subject of tidy evaluation or programming in dplyr. Your shiny input variable input$Grp is a string (as nirgrahamuk already mentioned) which you need to convert into a symbol to mimick typing y (as in your explicit example).