如何从 R Shiny selectInput() 中的列表中提取元素名称，而不是值?

Question

我想从 R Shiny 的selectInput()中用于choices参数的列表中提取元素名称，而不是特定值。

selectInput函数如下所示：

# ...
selectInput("xvar", "What is the predictor variable?",
choices = list("MPG" = "mpg",
"Cylinders" = "cyl",
"Engine Displacement" = "disp",
"Horse Power" = "hp",
"Gears" = "gear"),
# ...

在我的server.R代码中，我想使用，例如，"圆柱体"而不是"cyl"作为轴标签。例如(使用ggplot2(：

# ...
labs(x = input$xvar, y = input$yvar) +
# ...

names(input$xvar)返回NULL.有什么方法可以调用input$xvar并返回名称吗？

Answer 1

感谢保罗的评论、他提供的链接和这个 SO 线程，我能够回答我的问题。

下面我提供了旧的ui.R和server.R脚本，这些脚本生成了我不满意的轴标签，以及改进轴标签的新ui.R和server.R脚本。(新脚本中的更改标有# diff(

旧ui.R：

shinyUI(fluidPage(
titlePanel("Fit Regression Line for Chosen Variables and Points"),
sidebarLayout(
sidebarPanel(
h2("Model Specifics"), br(),
selectInput("xvar", "What is the predictor variable?",
choices = list("MPG" = "mpg",
"Cylinders" = "cyl",
"Engine Displacement" = "disp",
"Horse Power" = "hp",
"Gears" = "gear"),
multiple = FALSE),
selectInput("yvar", "What is the outcome variable?",
choices = list("MPG" = "mpg",
"Cylinders" = "cyl",
"Engine Displacement" = "disp",
"Horse Power" = "hp",
"Gears" = "gear"),
multiple = FALSE, selected = "cyl"),
h4("Intercept"), textOutput("int"),
h4("Slope"), textOutput("slope")
),
mainPanel(
br(), h2("Display"), h4("Drag to select which points to include in model"),
plotOutput("plot", brush = brushOpts(id = "brush1"))
)
)
))

旧server.R：

shinyServer(function(input, output) {
model <- reactive({
points <- brushedPoints(mtcars, brush = input$brush1,
xvar = input$xvar,
yvar = input$yvar)
if(nrow(points) <= 1) {
return(NULL)
} else {
lm(as.formula(paste0(input$yvar,
"~", input$xvar)),
data = points)
}
})
output$int <- renderText({
if(is.null(model())) {
"Too few data points selected"
} else {
round(model()[[1]][1], 2)
}
})
output$slope <- renderText({
if(is.null(model())) {
"Too few data points selected"
} else {
round(model()[[1]][2], 2)
}
})
output$plot <- renderPlot({
library(ggplot2)
ggplot(mapping = aes(x = mtcars[, input$xvar],
y = mtcars[, input$yvar])) +
theme_minimal() +
geom_point() +
labs(x = input$xvar, y = input$yvar) +
coord_cartesian(x = c(0, 1.2*max(mtcars[, input$xvar])),
y = c(0, 1.2*max(mtcars[, input$yvar]))) +
if(!is.null(model())) {
geom_abline(intercept = model()[[1]][1], slope = model()[[1]][2],
colour = "red", lwd = 2, alpha = 0.3)
}
})
})

脚本中的更改标有# diff

新ui.R：

shinyUI(fluidPage(
titlePanel("Fit Regression Line for Chosen Variables and Points"),
sidebarLayout(
sidebarPanel(
h2("Model Specifics"), br(),
uiOutput("si_xvar"), # diff
uiOutput("si_yvar"), # diff
h4("Intercept"), textOutput("int"),
h4("Slope"), textOutput("slope")
),
mainPanel(
br(), h2("Display"), h4("Drag to select which points to include in model"),
plotOutput("plot", brush = brushOpts(id = "brush1"))
)
)
))

新server.R：

shinyServer(function(input, output) {
varlist <- list("MPG" = "mpg",  # diff
"Cylinders" = "cyl",
"Engine Displacement" = "disp",
"Horse Power" = "hp",
"Gears" = "gear")
output$si_xvar <- renderUI(     # diff
selectInput("xvar", "What is the predictor variable?",
choices = varlist,
multiple = FALSE)
)
output$si_yvar <- renderUI(     # diff
selectInput("yvar", "What is the outcome variable?",
choices = varlist,
multiple = FALSE, selected = "cyl")
)
model <- reactive({
points <- brushedPoints(mtcars, brush = input$brush1,
xvar = input$xvar,
yvar = input$yvar)
if(nrow(points) <= 1) {
return(NULL)
} else {
lm(as.formula(paste0(input$yvar,
"~", input$xvar)),
data = points)
}
})
output$int <- renderText({
if(is.null(model())) {
"Too few data points selected"
} else {
round(model()[[1]][1], 2)
}
})
output$slope <- renderText({
if(is.null(model())) {
"Too few data points selected"
} else {
round(model()[[1]][2], 2)
}
})
output$plot <- renderPlot({
library(ggplot2)
ggplot(mapping = aes(x = mtcars[, input$xvar],
y = mtcars[, input$yvar])) +
theme_minimal() +
geom_point() +
labs(x = names(which(input$xvar == varlist)),       # diff
y = names(which(input$yvar == varlist))) +     # diff
coord_cartesian(x = c(0, 1.2*max(mtcars[, input$xvar])),
y = c(0, 1.2*max(mtcars[, input$yvar]))) +
if(!is.null(model())) {
geom_abline(intercept = model()[[1]][1], slope = model()[[1]][2],
colour = "red", lwd = 2, alpha = 0.3)
}
})
})