使用Reactive（）创建动态数量的FlexDashboard选项卡

Question

我想知道是否可以在FlexDashboard中创建许多标签，这些选项卡会根据某些用户输入而更改。作为玩具示例，我正在尝试绘制用户选择数据集的每个数字列的直方图，每个数字列都可以使用自己的直方图。如果用户更改数据集，则仪表板应更新和增加选项卡中的选项卡数，如果新选择的数据集中的数字列的数量更改。为简单起见，我只包含两个数据集。

---
title: "Reactive GGPlot Tabs"
output: 
  flexdashboard::flex_dashboard:
    theme: 
      version: 4
      bootswatch: cosmo
runtime: shiny
---

```{r}
pacman::p_load(tidyverse, shiny, flexdashboard)
```

Sidebar {.sidebar}
-------------------------------------

<h5>Required Input</h5>

```{r}
selectInput(inputId = "dataset", label = "Data:",
            choices = c('mtcars', 'iris'), selected = 'iris')


dataset = reactive({
  set = as.character(input$dataset)
  if(set=='iris'){data = iris} else{data = mtcars}
  return(data)
  })
```



```{r setup}
chart = reactive({
data = dataset()

num_cols <- unlist(lapply(data, is.numeric))
data = data[,num_cols] # only keep numeric columns for histogram

labels <- data %>% names # these will serve as labels for each tab

chart <- purrr::map(.x = data, ~ggplot(data, aes(x=.x))+geom_histogram()+theme_bw()) %>% setNames(labels) # assign names to each element to use later as tab titles

return(chart)
})
```



## Column {.tabset .tabset-fade}


```{r}
out <- reactive({
  lapply(seq_along(chart()), function(i) {
  
  a1 <- knitr::knit_expand(text = sprintf("### %s\n", names(chart())[i])) # tab header, auto extracts names of `chart`, %s indicates string
  
  a2 <- knitr::knit_expand(text = "\n```{r, message = F, warning = F}") # start r chunk
  
  a3 <- knitr::knit_expand(text = sprintf("\nchart()[[%d]]", i)) # extract graphs by "writing" out `chart[[1]]`, `chart[[2]]` etc. to be rendered later, %d indicates integer variable
  
  a4 <- knitr::knit_expand(text = "\n```\n") # end r chunk
  
  paste(a1, a2, a3, a4, collapse = '\n') # collapse together all lines with newline separator
})
  })
```

`r reactive({knitr::knit(text = paste(out(), collapse = '\n'))})`

运行此代码时，仪表板将显示Markdown块代码，但不会呈现图或选项卡。

我能够看到该代码在没有反应性的情况下使用该代码工作，但是根据所选数据集，我需要标签数来增加/减少。另外，我不允许使用facet_wrap。

这可能吗？