如何在 Rmarkdown 中从 R reticulate 调用 Python 函数

Question

我有这个 Rmarkdown，带有 python 函数：

---
title: "An hybrid experiment"
output: 
  flexdashboard::flex_dashboard:
    orientation: columns
    vertical_layout: fill
runtime: shiny
---

    ```{r setup, include=FALSE}
    library(flexdashboard)
    library(reticulate)
    ```

    ```{r}
    selectInput("selector",label = "Selector",
      choices = list("1" = 1, "2" = 2, "3" = 3),
      selected = 1)
    ```

    ```{python}
    def addTwo(number):
      return number + 2
    ```

我尝试在反应式上下文中使用函数addTwo，所以我尝试了这个：

    ```{r}
    renderText({
      the_number <- py$addTwo(input$selector)
      paste0("The text is: ",the_number)
    })
    ```

但是我收到了这个错误：

TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

Detailed traceback:
  File "<string>", line 2, in addTwo

我一定是做错了什么，请你指导我解决这个问题吗？

Answer 1

reticulate部分没问题，错误其实来自shiny。

这里有一些关于input$selector的重要细节：

• 应该事先用selectInput定义
• 需要用as.numeric转换成数字
• 如果尚未完成选择，req(input$selector) 将避免renderText 中的错误

这行得通：

---
title: "An hybrid experiment"
output: 
  flexdashboard::flex_dashboard:
    orientation: columns
    vertical_layout: fill
runtime: shiny
---

```{r setup, include=FALSE}
library(flexdashboard)
library(reticulate)
```

```{python}
def addTwo(number):
  return number + 2
```

```{r}
selectInput("selector",label = "Selector",
      choices = list("choose 1" = 1, "choose 2" = 2, "choose 3" = 3),
      selected = 1)

renderText({
      the_number <- py$addTwo(as.numeric(input$selector))
      paste0("The text is: ",the_number)
})
```