How to select a column from a dynamic input variable?

Question

I'm using flexdashboard and shiny to choose which variable to plot:

varSelectInput("button_var_fir"
               , "Select first num variable"
               , data = df_scat,
                multiple = FALSE
               )

ggplot(df_scat, aes(x = !!input$button_var_fir, y = Gen_type, fill = stat(x))) +
  geom_point(size= 3, alpha = .075)

it works fine, so far. My problem is, that I would like to subset the data e.g via

df$variable > 0
ggplot(df_scat, aes(x = df$!!input$button_var_fir > 0, y = Gen_type, fill = stat(x))) +
      geom_point(size= 3, alpha = .075)

but this doesn't work due to the $!!. How can I solve this?

Could you add a simple app to run? I personally prefer .data[[col]] or {{col}} or aes_string. Also maybe you need !!! or sym before? — NelsonGon
– NelsonGon, Commented Mar 16, 2022 at 10:51
I think this is not about running an app. It is about the question 'How do you select a column from a dataframe which name you have as a string in a variable?'. (Or maybe I don't understand the question.) — Georgery
– Georgery, Commented Mar 16, 2022 at 10:55
@Georgery No, you're right, I'm testing your advice atm. Tbh, I didn't understand NelsonGon's advice :) — Ben
– Ben, Commented Mar 16, 2022 at 10:57
NelsonGon is right. Inside a ggplot() call, you use one of the two options he gave to dynamically call the variable. Just replace col with input$button_var_fir. — Dan Adams
– Dan Adams, Commented Mar 16, 2022 at 11:58

Dan Adams · Accepted Answer · 2022-08-04 00:06:50Z

2

In {ggplot2}, which uses tidy evaluation, you can use the .data pronoun to dynamically select variables. It's nicely explained outside the {shiny} context in this answer too. This doesn't apply in {plotly} so you can either select with x = data[[input$column]] or x = get(input$column). This is also explained in this question.

Here's a small example to demonstrate how to do this for each plotting function.

library(plotly)
library(tidyverse)
library(shiny)

nbins <- 10

ui <- fluidPage(titlePanel("Dynamic Variable Selection"),
                sidebarLayout(sidebarPanel(
                  selectInput(
                    inputId = "y1",
                    label = "Select variable",
                    choices = names(mtcars))),
                mainPanel(plotOutput(outputId = "ggplot"),
                          plotlyOutput(outputId = "plotly"))))

server <- function(input, output) {
  # dynamically pull variable in ggplot
  output$ggplot <- renderPlot({
    mtcars %>%
      ggplot(aes(x = .data[[input$y1]])) +
      geom_histogram(bins = nbins) +
      ggtitle("ggplot")})
  # dynamically pull variable in plotly
    output$plotly <- renderPlotly({
    mtcars %>%
        plot_ly(x = .[[input$y1]], type = "histogram", nbinsx = nbins) %>% 
        layout(title = list(text = "Plotly"),
               xaxis = list(title = input$y1))
      })
    }

shinyApp(ui = ui, server = server)

edited Aug 4, 2022 at 0:06

answered Mar 16, 2022 at 16:37

Dan Adams

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2 Comments

Ben Over a year ago

thanks a lot but tbh, I lack a bit understanding. Is this only working for shiny or ggplot? I mean I asked for it but I'm currently trying to use it for plot_ly as well but I can't get it run?

Dan Adams Over a year ago

I don't think this would work for plotly. This is unique to tidy-eval. Please edit your question to expand the scope and clarify the use case and we can help further.

Georgery · Accepted Answer · 2022-03-16 14:54:16Z

0

Maybe what you want is

df[[input$button_var_fir]] > 0

instead of df$!!input$button_var_fir > 0.

Addition:
You want to subset the data that goes into the plot, right? What I would actually do is subsetting the dataframe itself before it goes into the plot function. When you use the tidyverse this could be what you want:

df_scat %>%
    filter(!!input$button_var_fir > 0) %>%
    ggplot(aes(x = !!input$button_var_fir, y = Gen_type, fill = stat(x))) +
    geom_point(size= 3, alpha = .075)

edited Mar 16, 2022 at 14:54

answered Mar 16, 2022 at 10:51

Georgery

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6 Comments

Ben Over a year ago

As far as I see this yields logical values (False, True) inside the plot

Dan Adams Over a year ago

I think you need to replace df with .data and then it should work.

Ben Over a year ago

unfortunately, it doesn't :) you mean "df.data[[input$button_var_fir]]", right?

Dan Adams Over a year ago

No, just .data. that's the generic way if referring to whatever data you passed to ggplot()

Dan Adams Over a year ago

Works inside any tidy-eval function including many {dplyr} functions. See here for more info on the .data pronoun. More generally this blog post gives a nice overview of how curly-curly ({{}}) is replacing the old quote-unquote method (!!sym("x")).

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