ewall(parse(text ="f")))在Shinypass.io上 [英] eval(parse(text="f")) on shinypass.io

问题描述

我想编写一个应用程序，使用户可以使用textInput输入功能，然后对该功能执行某些操作.这是一个玩具示例:

I want to write an app that lets the user enter a function using textInput, and then does something with the function. Here is a toy example:

shinyUI(fluidPage(
   titlePanel("Test"),
  sidebarLayout(
     sidebarPanel(
        textInput("fun","function:",value="x")
    ),
  mainPanel(
      uiOutput("text")
  )
)

shinyServer(function(input, output) {
  findMax <- reactive({
       f <- function(x) eval(parse(text = input$fun), envir = list(x))
       x < seq(0,1,length=100)
       max(f(x)) 
   })  
   output$text <- renderText( {   
       findMax()
    })     

  })
))

，这在我的本地计算机上运行时效果很好.但是，当我将其提交给shinyapps.io时，出现错误:找不到对象x.似乎eval的envir参数存在问题，但我无法找出它是什么.

and this works just fine when run on my computer locally. But when i submit it to shinyapps.io i get the error: object x not found. It seems there is a problem with the envir argument of eval, but i have not been able to find out what it is.

当然，一般来说，关于eval(parse())构造有很多讨论，因此，如果有人对如何执行此操作有建议(具有在框中键入表达式并将其翻转的功能)进入一个函数)，我也将不胜感激.

There is of course a lot of discussion on the eval(parse()) construct in general, so if anyone has a suggestion on how to do this (have the ability to type in an expression in a box and get it turned into a function) differently i would also be grateful.

狼帮

推荐答案

尝试了许多事情之后，我终于使这一工作了:

After trying a number of things i finally got this one to work:

代替

f <- function(x) eval(parse(text = input$fun), envir = list(x))

使用

eval(parse(text = paste("f <- function(x)",input$fun,sep="")))

我不知道为什么两者都可以在本地计算机上运行，​​但是只有第二个可以在Shinyapps.io上运行.另外，如果有人有其他方法可以做到这一点，我仍然会很感兴趣.

i have no idea why both work on my computer locally but only the second works on shinyapps.io . Also, i would still be interested if anyone has a different way to do this.

狼帮

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