使用 switch 从 ggplot2 函数内转换变量

Question

我有一个 R Shiny 应用程序，它根据用户选择的 x 变量绘制数据集horsepower。mtcars我希望用户能够在绘图之前选择对 x 变量执行的转换。在下面的简化示例中，这些变换是能够对其求平方或获得其倒数的能力。我正在使用开关功能来执行此操作。

虽然这个切换函数在非闪亮的上下文中工作，但我无法让它在工作的闪亮应用程序中执行。我知道我可以对数据框的反应式副本执行转换并从中进行绘图，但如果可能的话，我想在 ggplot 调用本身中执行转换。有人对如何做到这一点有任何建议吗？

library(shiny)
library(tidyverse)

tran_func <- function(pred, trans) {
  switch(trans,
         "None" = pred,
         "Reciprocal" = 1/pred,
         "Squared" = pred^2,
  )
}

ui <- fluidPage(
  selectInput("xvar",
              "Select X Variable",
              choices = names(mtcars),
              selected = "disp"),
  selectInput("transform",
              "Select Transformation",
              choices = c("None", "Reciprocal", "Squared"),
              selected = "None"),
  plotOutput("scatter_good"),
  plotOutput("scatter_bad")
)

server <- function(input, output, session) {
  output$scatter_good <- renderPlot({
   mtcars %>% 
    ggplot(aes_string(x = "hp", y = input$xvar)) +
    geom_point()
  })
  output$scatter_bad <- renderPlot({
    mtcars %>% 
      ggplot(aes_string(x = "hp", y = tran_func(input$xvar, "Squared"))) +
      geom_point()
  })
}

shinyApp(ui, server)

Answer 1

问题是对传递来input$xvar修改列的字符串进行评估。一个选项是将“数据”也作为函数中的参数传递，并用于[[对列进行子集化，而不转换为符号或求值

library(shiny)
library(ggplot2)
library(dplyr)
tran_func <- function(data, pred, trans) {
  switch(trans,
         "None" = data[[pred]],
         "Reciprocal" = 1/data[[pred]],
         "Squared" = data[[pred]]^2,
  )
}

ui <- fluidPage(
  selectInput("xvar",
              "Select X Variable",
              choices = names(mtcars),
              selected = "disp"),
  selectInput("transform",
              "Select Transformation",
              choices = c("None", "Reciprocal", "Squared"),
              selected = "None"),
  plotOutput("scatter_good"),
  plotOutput("scatter_bad")
)

server <- function(input, output, session) {
  output$scatter_good <- renderPlot({
    mtcars %>%
      mutate(y_col = tran_func(cur_data(), input$xvar, input$transform)) %>%
      ggplot(aes(x = hp, y = y_col)) +
      geom_point()
  })
  
  output$scatter_bad <- renderPlot({
    mtcars %>% 
      mutate(y_col = tran_func(cur_data(), input$xvar, input$transform)) %>%
      ggplot(aes(x = hp, y =y_col)) +
      geom_point()
  })
  
}

shinyApp(ui, server)

-输出