R shiny invalid formula - r

Question

I have a problem. I want to use sidebar to curb time series plot, however, I get invalid formula error when trying to do the plot. Can someone pls help?
server.r
library(shiny)
library(BCA)
data(Eggs)
# Define server logic required to plot
shinyServer(function(input, output) {
formulaX <- reactive({
tmp <- paste(input$range,collapse = ":")
paste("Eggs[",tmp,",1]")
})
formulaY <- reactive({
tmp1 <- paste(input$range,collapse = ":")
paste("Eggs[",tmp1,",5]")
})
# Return the formula text for printing as a caption
output$caption <- renderText({
paste(formulaX(),formulaY(),sep = " ")
})
#creating plot -ERROR
output$mpgPlot <- renderPlot({
plot(as.formula(formulaX()),as.formula(formulaY()))
})
})
ui.r
library(shiny)
# Define UI
shinyUI(pageWithSidebar(
# Application title
headerPanel("Eggs"),
sidebarPanel(
# Specification of range within an interval
sliderInput("range", "Range:",
min = 1, max = 105, value = c(20,50))
),
mainPanel(
h3(textOutput("caption")),
plotOutput("mpgPlot")
)
))

Answer 1

"Eggs[1:10,1]" is not a formula, it is a character-representation of a subset. Since you are always choosing columns 1 and 5, your "formula" is always "Cases ~ Week" (I don't have BCA installed, I think that's correct), and you are intending to use a subset of rows from the data.
Perhaps this would work instead (hasty, some programming safeguards would be appropriate):
# no need for formulaX(), formulaY()
# not certain what you want/need from output$caption
dataX <- reactive({ Eggs[input$range[1]:input$range[2],,drop = FALSE] })
and your plot:
output$mpgPlot <- renderPlot({
plot(Cases ~ Week, data = dataX())
})
or
output$mpgPlot <- renderPlot({
x <- dataX()
plot(x$Week, x$Cases)
})