Passing on data and input within a shiny app - r

Question

I was trying to simplify my shiny app. However, as much as I try it is not working, as I would like it to.
My Idea was to load data to the app, perform some analyses and return intermediate results to the user. At the moment I have to load the data, choose the right columns etc. for each output I am generating:
ui <- shinyServer(
fluidPage(
tabsetPanel(
tabPanel("Data upload",
titlePanel("Data upload"),
sidebarLayout(
sidebarPanel(
fileInput("file1", "Choose CSV File",multiple = TRUE, accept = c("text/csv","text/comma-separated-values,text/plain",".csv")),
tags$hr(),
checkboxInput("header", "Header", TRUE), radioButtons("sep", "Separator", choices = c(Comma = ",", Semicolon = ";",Tab = "\t"), selected = ","),
tags$hr(),
checkboxInput("disp", "Display",TRUE),
tags$hr(),
uiOutput("choose_first_column"),
uiOutput("choose_second_column"),
br()
),
mainPanel(
tableOutput("contents"),
tags$hr(),
tableOutput("tab")
)
)
),
tabPanel("2","2"
)
)
)
)
server <- shinyServer(
function(input, output) {
observe({
req(input$file1)
df <- read.csv(input$file1$datapath,
header = input$header,
sep = input$sep,
quote = input$quote)
output$contents <- renderTable({
(head(df))})
output$choose_first_column <- renderUI({
colnames <- names(df)
selectInput("column_1", "Choose Date column",
choices = colnames,
selected = colnames)})
output$choose_second_column <- renderUI({
colnames <- names(df)
selectInput("column_2", "Choose Variable column",
choices = colnames,
selected = colnames)})
output$tab <- renderTable({
req(input$file1)
df2 <- read.csv(input$file1$datapath,
header = input$header,
sep = input$sep,
quote = input$quote)
df2 <- df2[, c(input$column_1,input$column_2), drop = FALSE]
return(head(df2))})
})
})
runApp(list(ui = ui, server = server))
It works, but as I usually have many data and I want to perform a couple of analyses, it is gets quite time-consuming to load and process the data for each “output content”.
Is there a way to avoid this? Could I for example load the data and choose the right columns globaly, as in the second example? (I crossed out the lines where the error occurs)
ui <- shinyServer(
fluidPage(
tabsetPanel(
tabPanel("Data upload",
titlePanel("Data upload"),
sidebarLayout(
sidebarPanel(
fileInput("file1", "Choose CSV File",multiple = TRUE, accept = c("text/csv","text/comma-separated-values,text/plain",".csv")),
tags$hr(),
checkboxInput("header", "Header", TRUE), radioButtons("sep", "Separator", choices = c(Comma = ",", Semicolon = ";",Tab = "\t"), selected = ","),
tags$hr(),
checkboxInput("disp", "Display",TRUE),
tags$hr(),
uiOutput("choose_first_column"),
uiOutput("choose_second_column"),
br()
),
mainPanel(
tableOutput("contents"),
tags$hr(),
tableOutput("tab")
)
)
),
tabPanel("2","2"
)
)
)
)
server <- shinyServer(
function(input, output) {
observe({
req(input$file1)
df <- read.csv(input$file1$datapath,
header = input$header,
sep = input$sep,
quote = input$quote)
output$contents <- renderTable({
(head(df))})
output$choose_first_column <- renderUI({
colnames <- names(df)
selectInput("column_1", "Choose Date column",
choices = colnames,
selected = colnames)})
output$choose_second_column <- renderUI({
colnames <- names(df)
selectInput("column_2", "Choose Variable column",
choices = colnames,
selected = colnames)})
# df <- df[, c(input$column_1,input$column_2), drop = FALSE]
#
# output$tab <- renderTable({
# (head(df))})
})
})
runApp(list(ui = ui, server = server))
Input data example:
date time level
01.01.2000 00:00:00 0.3724
01.01.2000 01:00:00 0.192
01.01.2000 02:00:00 -0.0252
I would appreciate any help!
Aishe

Answer 1

From what I've understood, you are getting an error because the dataframe df that you have defined is not reactive. You should make it reactive as it will change every time the user selects input columns.
Refer this to read about reactivity. Change the deleted portion of your code to this:
df.selected.columns <- df[c(input$column_1,input$column_2)]
output$tab <- renderTable({
(head(df.selected.columns()))
})