Error when selecting variables (with `varSelectInput`) and using ggplot with Shiny (Error: `arg` must a symbol)

Question

I am trying to make a Shiny app which uses this function (made in R markdown):

ls_vs <- function(variable) {
dataset %>%
  filter({{variable}} != 254.948530) %>% 
  filter({{variable}} != 121.738080) %>%
  ggplot(mapping = aes(y = life_satisfaction, x = {{variable}})) +
  geom_point(aes(color = region, shape = freedom_status), size = 2) +
  geom_smooth(color = "cyan") +
  labs(y = "Life Satisfaction", shape = "Freedom Status", color = "Continent")
}

ls_vs(economic_freedom)

I am getting the desired results with this function:

Now Here's my attempt of integrating that into a shiny app:

The UI section:

tabPanel("Factor Comparision", 
               
               sidebarPanel(
                 varSelectInput(inputId = "variable", label = "Select Factor to Compare", data = dataset),
                 
                mainPanel(                                   
                  h1("Test"),           
                  plotOutput("ls_vs"),
                 )   
               )),

And here is the server section:

#Factor Comparisons
    output$ls_vs <- renderPlot({
      dataset%>%
        filter({{input$variable}} != 254.948530) %>% 
        filter({{input$variable}} != 121.738080) %>%
        ggplot(mapping = aes(y = life_satisfaction, x = {{input$variable}})) +
        geom_point(aes(color = region, shape = freedom_status), size = 2) +
        geom_smooth(color = "cyan") +
        labs(y = "Life Satisfaction", shape = "Freedom Status", color = "Continent")
    })

Upon trying to run the app, I'm getting the error:

Error: arg must a symbol

Have I done something incorrectly in the UI area or in the sever area? How does one correctly use varSelectInput in Shiny to make an interactive ggplot where one can change the variable to change the plot?

Thank you very much!

Ronak Shah · Accepted Answer · 2021-12-13 04:21:03Z

1

The main difference between the code in markdown vs that in Shiny is Shiny passes string value of the variable ("economic_freedom") whereas the function in markdown has been written to work with bare column names (economic_freedom).

Change the function to work with strings that can be done using .data instead of {{}}.

library(dplyr)
library(ggplot2)

output$ls_vs <- renderPlot({
  dataset%>%
    filter(.data[[input$variable]] != 254.948530) %>% 
    filter(.data[[input$variable]] != 121.738080) %>%
    ggplot(mapping = aes(y = life_satisfaction, x = .data[[input$variable]])) +
    geom_point(aes(color = region, shape = freedom_status), size = 2) +
    geom_smooth(color = "cyan") +
    labs(y = "Life Satisfaction", shape = "Freedom Status", color = "Continent")
})

answered Dec 13, 2021 at 4:21

Ronak Shah

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2 Comments

BoyAcc Over a year ago

Thank you so much, it worked well. I have a quick follow up question, would you be able to offer some guidance on removing certain options from varSelectInput. My app shows the drop down menu with ALL variables, but I want to select only a specific set of variables to be shown in the drop down menu and hopefully rename them so they don't show up with underscores if possible. Thank you again.

Ronak Shah Over a year ago

You can pass subset of dataframe in varSelectInput i.e instead of passing data only pass dataset[1:5] if you want to include first 5 columns. You may also use selectInput instead of varSelectInput. In selectInput you can pass the values manually like c('A', 'B', 'C')` or subset of column names like names(dataset)[1:5].

jpdugo17 · Accepted Answer · 2021-12-13 05:47:57Z

0

Using "bang bang" operator with dplyr::sym() should also work.

#Factor Comparisons
output$ls_vs <- renderPlot({
  dataset%>%
    filter(!!sym(input$variable) != 254.948530) %>% 
    filter(!!sym(input$variable) != 121.738080) %>%
    ggplot(mapping = aes(y = life_satisfaction, x = !!sym(input$variable))) +
    geom_point(aes(color = region, shape = freedom_status), size = 2) +
    geom_smooth(color = "cyan") +
    labs(y = "Life Satisfaction", shape = "Freedom Status", color = "Continent")
})

answered Dec 13, 2021 at 5:47

jpdugo17

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