R，Shiny：子集 dataframe 基于具有反应列名称的条件

Question

Using R/Shiny, I'd like to graph a variable chosen by the user, but for values below a certain threshold.

I know that it is possible to do the filtering using ggplot, but for various reason, I'd like the dataframe to be reactively subsetted. In my example below, I'd like rv$m to be subsetted based on the column chosen by the user. Based on this answer , I tried to filter based on colnames, but to no avail. I also tried various other solutions gleaned here and ther (without much understanding them), see below.

# Test of shiny app for a histogram
library(shiny)
library(ggplot2)
library(dplyr)
dataForPlot <- iris

# Define UI for app that draws a histogram ----
ui <- fluidPage(
  selectInput(inputId = "dimToPlot", label="Dim to plot:",choices = c("Length","Width")),
  plotOutput(outputId = "distPlot")
 )

# Define server logic required to draw a histogram ----
server <- function(input, output) {

  rv <- reactiveValues()
  observeEvent(input$dimToPlot,{

    rv$colName <- paste0("Petal.",input$dimToPlot) # variable that will be displayed
    rv$mfull <- dataForPlot[rv$colName] # dataframe subsetted to the proper var, ALL OBS

    # All the ways that I could not make work
    rv$m <- rv$mfull[rv$mfull[colnames(rv$mfull)==rv$colName] <2, ]
    rv$m <- subset(rv$mfull, !!get(rv$colName) <2, select = c(rv$colName)) 
    rv$m <- rv$mfull %>% dplyr::filter(!!rv$colName  <2)

  })

  # Histogram  ----
  output$distPlot <- renderPlot({
      ggplot(environment = environment(),
        data=rv$m, aes(x=.data[[rv$colName]])) + 
        geom_histogram(color="white", fill="#2b6a6c",bins = 10,boundary=0   ) 
  })

}

# Create Shiny app ----
shinyApp(ui = ui, server = server)

Answer 1

Here is a proposal; I have simplified your code to define a global data() reactive expression, which is the subset that you want. This subset changes every time the user picks a new variable, via the eventReactive .

# Test of shiny app for a histogram
library(shiny)
library(ggplot2)
library(dplyr)
dataForPlot <- iris

# Define UI for app that draws a histogram ----
ui <- fluidPage(
  selectInput(inputId = "dimToPlot", label="Dim to plot:",choices = c("Length","Width")),
  plotOutput(outputId = "distPlot")
)

# Define server logic required to draw a histogram ----
server <- function(input, output) {

  column <- reactive({paste0("Petal.",input$dimToPlot)})
  data <- eventReactive(input$dimToPlot, {
    dataForPlot %>% 
      select(column()) %>%
      filter(get(column()) < 2)
  })

  # Histogram  ----
  output$distPlot <- renderPlot({
    ggplot(environment = environment(),
           data = data(), 
           aes_string(x = column())) +
      geom_histogram(color="white", fill="#2b6a6c",bins = 10,boundary=0) 
  })

}

# Create Shiny app ----
shinyApp(ui = ui, server = server)