How to select a column from a dynamic input variable? - r

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?

Answer 1

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)

Answer 2

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)