calculate different category based on numeric input

Question

I'm trying to make a web application using Rshiny which automatically calculates the titration rate of the infusion pump based on the drug dose and body weight. I have provided the formula for it in the attached google sheet file, but I'm having trouble making the web app version.

https://docs.google.com/spreadsheets/d/1Lu3Kquqw7b2wmwo_zk1jkpZ_1q0DVv0Pp06ToVOPslk/edit#gid=2092967400

The "drug_dose" data that I used in the code, is in sheet 2 of this file

here is the shiny R code I tried to make, but it doesn't work.

ui <- fluidPage( tabPanel("Drugu dose",
                          # Give the page a title
                          titlePanel("Drug dose"),
                          helpText("calculates the titration rate of the infusion pump based on the drug dose and body weight"),
                          # left input 
                          sidebarPanel(
                              numericInput(inputId = "bw", label = "body weight"),
                              checkboxGroupInput(inputId = "drug", label = "drug type", choices = c("Noradrenalin/vascon (4mg/50 cc)", 
                                                                                                     "NTG (50mg/50cc)"),
                              
                          ),
                          
                          
                          
                          # right outputs
                          mainPanel(br(),
                                    # h3("Results"),
                                    br(),
                                    tableOutput("table1"), width=6 )
                          
)))


#
server <- shinyServer(function(input,output){
    if(input$drug == "Noradrenalin/vascon (4mg/50 cc)")
    {data <- drug_dose
    data$dose <- data$dose_base * input$bw*60/80
    
    df_subset <- reactive({
        a <- subset(data, drug == input$drug)
        return(a)
    })
    
    output$table1 <- renderTable(df_subset$dose_base, df_subset$dose)
    }
    else if (input$drug == "NTG (50mg/50cc)")
    {data <- drug_dose
    data$dose <- data$dose_base * input$bw*60/1000
    
    df_subset <- reactive({
        a <- subset(data, drug == input$drug)
        return(a)
    })
    
    output$table1 <- renderTable(df_subset$dose_base, df_subset$dose)
    }
    
    
}) 


shinyApp(ui = ui, server = server)

it says in the description that I need the active reactive context, but I'm not sure where and how to put the active reactive context.

I really appreciate your help, thank you

Answer 1

Besides some minor issues with your code, e.g. a numericInput requires a value the main issue is that you could use e.g. input$drug only within a so-called reactive. Moreover your code you be simplified, as there is no need for an if statement:

library(shiny)

ui <- fluidPage(
  tabPanel(
    "Drugu dose",
    # Give the page a title
    titlePanel("Drug dose"),
    helpText("calculates the titration rate of the infusion pump based on the drug dose and body weight"),
    # left input
    sidebarPanel(
      numericInput(inputId = "bw", label = "body weight", value = 60),
      checkboxGroupInput(inputId = "drug", label = "drug type", 
                         choices = unique(drug_dose$drug)),
      # right outputs
      mainPanel(br(),
        # h3("Results"),
        br(),
        tableOutput("table1"),
        width = 6
      )
  )
  )
)

server <- function(input, output) {
  df_subset <- reactive({
    data <- subset(drug_dose, drug %in% input$drug)
    data$dose <- data$dose_base * input$bw * 60 / 80
    data
  })
  
  output$table1 <- renderTable({
    df_subset()
  })
}

shinyApp(ui = ui, server = server)
#> 
#> Listening on http://127.0.0.1:7317

^{Created on 2021-08-14 by the reprex package (v2.0.1)}

DATA

drug_dose <- data.frame(
  stringsAsFactors = FALSE,
  dose_base = c(
    0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
    0.7, 0.8, 0.9, 0.05, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2,
    2.25, 2.5
  ),
  drug = c(
    "Noradrenalin/vascon (4mg/50 cc)", "Noradrenalin/vascon (4mg/50 cc)",
    "Noradrenalin/vascon (4mg/50 cc)", "Noradrenalin/vascon (4mg/50 cc)",
    "Noradrenalin/vascon (4mg/50 cc)",
    "Noradrenalin/vascon (4mg/50 cc)", "Noradrenalin/vascon (4mg/50 cc)",
    "Noradrenalin/vascon (4mg/50 cc)", "Noradrenalin/vascon (4mg/50 cc)",
    "Noradrenalin/vascon (4mg/50 cc)", "NTG (50mg/50cc)",
    "NTG (50mg/50cc)", "NTG (50mg/50cc)", "NTG (50mg/50cc)",
    "NTG (50mg/50cc)", "NTG (50mg/50cc)", "NTG (50mg/50cc)",
    "NTG (50mg/50cc)", "NTG (50mg/50cc)"
  )
)