in shiny, How to insert math symbols in a text input so that my r code performs the equations?

Question

I have built a shiny app in which my inputs only recognize numeric values. For example, in the text box I insert 2^7 and it doesn´t perform the procedure in my function from the R code. On the other hand if I insert 128 it does perform the procedure.

library(shiny)
library(shinythemes)
library(shinydashboard)
library(stringr)
library(ggplot2)     

ui = navbarPage(

  theme = shinytheme("superhero"),
  title = "Generador de Numeros Aleatorios",
         tabPanel(title = h5("Generadores"),

sidebarPanel(
  selectInput("metodo", "Selecciona el m?todo",
              selected= "Multiplicativo",
              choices = c("Multiplicativo","Lineal","SimuladorR")
  ),
  textInput("z0","Ingresa una semilla:",value = 3),
  texticInput("n","Ingresa 'n':",value=10),
  textInput("a","Ingresa 'a':",value=2),
  textInput("m","Ingresa 'm':", value=15),
  textInput("c","Ingresa 'c':",value=10),
  actionButton("generador", label = "Generar"),
  br(),
  radioButtons("type", "Formato de descarga:",
               choices=c("Excel(CVS)", "Text(TSV)"),selected = "Excel(CVS)", inline=T),
  helpText("Click en el boton de Exportar para descragar los datos."),
  downloadButton('downloaddata','Exportar')

  #downloadButton("exportador", label = "Exportar")
  #actionButton("exportador", label = "Exportar"),
  #br(),
  #helpText("Click en el boton de Exportar para descargar los datos"),

), #Cierra sidebarPanel


mainPanel(
  h5("Valores Generados:"),
  plotOutput("grafica"),
  tableOutput("tablaValores")
) #Cierra mainPanel

   ),   

server = function(input, output,session){



 ## Generador Multiplicativo
  Congruencial.Multiplicativo = function(z0,a,m,n){
   z<-c()
   u<-c()
   z[1]<-z0
   u[1]<-z[1]/m

   if(n>1){
     for (i in 1:n+1) {
       z[i]<-(a*z[i-1]) - floor((a*z[i-1])/m)*m
     }

     for(i in 1:n+1){
       u[i]<-z[i]/m
     }

   }

   return(u[-1])
  }

  ## Generador Lineal
  Congruencial.Lineal<-function(z0,m,a,c,n){
    z=c()
    k=c()
    u=c()

    z[1]=z0
    k[1]=floor(((a*z[1])+c)/m)


    for(i in seq(2,n+1,by=1)){

      z[i]=((a*z[i-1])+c)-(m*k[i-1])
      k[i]=floor(((a*z[i])+c)/m)
      u[i]=z[i]/m

      }

      return(u[-1])
  }

   ## Generador de R
    Simulador.R = function(n){
      r<-runif(n=n,min=0,max=1)
      return(r)
     }

   ### Ahora para mostrar los valores guardados:
   observeEvent(input$generador, { 


    output$grafica = renderPlot ({

      datos = valores()
      datos = as.data.frame(datos)

     ggplot(datos)+geom_histogram(aes(x=datos,y=..density..),
                               breaks=seq(0, 1, .01),closed="left",
                               color="white", fill="orange")+
       labs(title="Funcion de Densidad",
            x=" x ", 
            y = "Densidad"
        )+theme_bw()+
        scale_x_continuous(breaks =seq(0, 1, 0.1))+
        scale_y_continuous(breaks =seq(0, 1, 0.1))+
        stat_function(fun=dunif,xlim=c(-.5,1.5),size=1,color="red",
                  args =list(min=0, max=1) )

    })

   valores = reactive({ switch (input$metodo, 
   Multiplicativo = 
   Congruencial.Multiplicativo(input$z0,input$a,input$m,input$n),
   Lineal = Congruencial.Lineal(input$z0,input$m,input$a,input$c,input$n),
   SimuladorR = Simulador.R(input$n) )})   #Cierra valores


   numord = valores() #Llamamos los valores aleatorios generados
   mostrar = as.data.frame(cbind(seq(1,input$n,by=1),numord))
   colnames(mostrar)=c("i", "u")
   output$tablaValores = renderTable(mostrar)

  }) #Cierra observeEvent

Now this is part of the code in which I need the text input to be recognized as numeric so that the app can work. The values I need the app to read as a string and turn them into numeric are z0, n, m, c. I have tried to put them into the observe event and neither they work.

The app creates a series of semirandom values with generators, that need some entry values which are specified in the paragraph above.

Welcome to SO. To get help on this site it's best to include your data and the code you have attempted, so somebody can easily copy and paste into R to try to find a solution. Check out [this link](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) for more info. — astrofunkswag, Apr 04 '20 at 19:14

Ben · Accepted Answer · 2020-09-04T17:52:57.927

Here is a demo that might be helpful. You can input a character string, and then use eval(parse(text = ... to evaluate the expression.

library(shiny)

ui <- fluidPage(
  textInput("ti_math", "Enter formula:"),
  textOutput("to_result")
)

server <- function(input, output, session) {
  output$to_result <- renderText({
    eval(parse(text = input$ti_math))
  })
}

shinyApp(ui, server)

Disclaimer: while this should work, the assumption is that the app will be running locally. Using eval on user input can be a security risk. See this post for more information.

Edit: Thank you for providing additional code. I was not able to reproduce completely (missing valores()) but I think I can make a couple suggestions.

For z0, n, m, c, you can access the inputs through input$z0, etc.

Try this:

observeEvent(input$generador, { 
  z0 = eval(parse(text = input$z0))
  print(z0)
})

You should see in your console, that if you provide something like 3^4 for z0 it should show 81 and be numeric.

You could do the same for n, m, c - I'm guessing you might be accessing these variables in valores() or other reactive expression.

I also noticed you have output$grafica and output$tablaValores inside of your observeEvent - I would recommend moving them out of observeEvent. One strategy is to use something <- eventReactive(input$generador, {... and then call something() from plot and table outputs.

Edit: Thank you for providing valores(). I can now provide something more reproducible.

I included eval(parse(text = input$...)) for z0, n, a, m, c. This is inside valores() so that all functions using these values for calculations will be evaluated for mathematical symbols first.

Note that I moved the renderTable and renderPlot from observeEvent, and changed observeEvent to eventReactive which will be responsive to the action button.

I also changed ui and server to separate components, and then call shinyApp in the end (just a preference).

This does provide a table and plot when button pressed. Please let me know if this is closer.

library(shiny)
library(shinythemes)
library(shinydashboard)
library(stringr)
library(ggplot2)     

ui = navbarPage(
  
  theme = shinytheme("superhero"),
  title = "Generador de Numeros Aleatorios",
  tabPanel(title = h5("Generadores"),
           
           sidebarPanel(
             selectInput("metodo", "Selecciona el m?todo",
                         selected= "Multiplicativo",
                         choices = c("Multiplicativo","Lineal","SimuladorR")
             ),
             textInput("z0","Ingresa una semilla:",value = 3),
             textInput("n","Ingresa 'n':",value=10),
             textInput("a","Ingresa 'a':",value=2),
             textInput("m","Ingresa 'm':", value=15),
             textInput("c","Ingresa 'c':",value=10),
             actionButton("generador", label = "Generar"),
             br(),
             radioButtons("type", "Formato de descarga:",
                          choices=c("Excel(CVS)", "Text(TSV)"),selected = "Excel(CVS)", inline=T),
             helpText("Click en el boton de Exportar para descragar los datos."),
             downloadButton('downloaddata','Exportar')
             
             #downloadButton("exportador", label = "Exportar")
             #actionButton("exportador", label = "Exportar"),
             #br(),
             #helpText("Click en el boton de Exportar para descargar los datos"),
             
           ), #Cierra sidebarPanel
           
           
           mainPanel(
             h5("Valores Generados:"),
             plotOutput("grafica"),
             tableOutput("tablaValores")
           ) #Cierra mainPanel
           
  )
)

server = function(input, output,session){
    
    ## Generador Multiplicativo
    Congruencial.Multiplicativo = function(z0,a,m,n){

      z<-c()
      u<-c()
      z[1]<-z0
      u[1]<-z[1]/m
      
      if(n>1){
        for (i in 1:n+1) {
          z[i]<-(a*z[i-1]) - floor((a*z[i-1])/m)*m
        }
        
        for(i in 1:n+1){
          u[i]<-z[i]/m
        }
        
      }
      
      return(u[-1])
    }
    
    ## Generador Lineal
    Congruencial.Lineal<-function(z0,m,a,c,n){
      z=c()
      k=c()
      u=c()
      
      z[1]=z0
      k[1]=floor(((a*z[1])+c)/m)
      
      
      for(i in seq(2,n+1,by=1)){
        
        z[i]=((a*z[i-1])+c)-(m*k[i-1])
        k[i]=floor(((a*z[i])+c)/m)
        u[i]=z[i]/m
        
      }
      
      return(u[-1])
    }
    
    ## Generador de R
    Simulador.R = function(n){
      r<-runif(n=n,min=0,max=1)
      return(r)
    }
    
    valores = eventReactive(input$generador, { 
      
      z0 = eval(parse(text = input$z0))
      a = eval(parse(text = input$a))
      m = eval(parse(text = input$m))
      c = eval(parse(text = input$c))
      n = eval(parse(text = input$n))
      
      switch  (input$metodo, 
               Multiplicativo = Congruencial.Multiplicativo(z0,a,m,n),
               Lineal = Congruencial.Lineal(z0,m,a,c,n),
               SimuladorR = Simulador.R(n)
      )
    })   #Cierra valores
    
    output$tablaValores = renderTable({
      numord = valores() #Llamamos los valores aleatorios generados
      mostrar = as.data.frame(cbind(seq(1,input$n,by=1),numord))
      colnames(mostrar)=c("i", "u")
      mostrar
    })
    
    output$grafica = renderPlot ({
      
      datos = valores()
      datos = as.data.frame(datos)
      
      ggplot(datos)+geom_histogram(aes(x=datos,y=..density..),
                                   breaks=seq(0, 1, .01),closed="left",
                                   color="white", fill="orange")+
        labs(title="Funcion de Densidad",
             x=" x ", 
             y = "Densidad"
        )+theme_bw()+
        scale_x_continuous(breaks =seq(0, 1, 0.1))+
        scale_y_continuous(breaks =seq(0, 1, 0.1))+
        stat_function(fun=dunif,xlim=c(-.5,1.5),size=1,color="red",
                      args =list(min=0, max=1) )
      
    })
}
    
shinyApp(ui, server)

how can I use the function you suggested to then use the value registered for a function inside the server? — Pablo Cervantes, Apr 04 '20 at 23:13
have already edited my question, would really appreciate it if you can take a look — Pablo Cervantes, Apr 05 '20 at 00:18
I have already added valores, sorry for missing out on that. I have already tried doing what you suggested and it is not working as the warning says: non-numeric argument for binary operator — Pablo Cervantes, Apr 05 '20 at 17:13
I'm currently developing a package called `shinymath`. I'm adding some examples to do something that may be interesting to you https://github.com/tomicapretto/shinymath — Tomas Capretto, Nov 14 '20 at 00:16

score 1 · Answer 2 · answered Apr 06 '20 at 13:04

eval(text = parse(......)) works fine but it is dangerous. You can turn any string to an evaluated R command with this way, for example a command which deletes some files...

Since the strings you enter are mathematical expressions, you can use the Ryacas package to evaluate them. Ryacas will fail if the string is not a mathematical expression.

library(Ryacas)
.......

valores = eventReactive(input$generador, { 

  z0 = as.numeric(yac_str(sprintf("N(%s)", input$z0)))
  a = as.numeric(yac_str(sprintf("N(%s)", input$a)))
  m = as.numeric(yac_str(sprintf("N(%s)", input$m)))
  c = as.numeric(yac_str(sprintf("N(%s)", input$c)))
  n = as.numeric(yac_str(sprintf("N(%s)", input$n)))
  ......

in shiny, How to insert math symbols in a text input so that my r code performs the equations?

2 Answers2

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