Bruna Wundervald - 2 months ago 12
R Question

# plotting equations with restricted domains in shiny

there.
Im building an shiny app thats plots some functions. The user can modify the parameters. The problem appears when I have a restricted function, specially when its related to x. This is one example:

Sliders:

sliderInput("th19",
HTML("$$\\theta_1$$"),
min = 1,
max = 10,
value = 2)
sliderInput("thB9",
HTML("$$\\theta_b$$"),
min = 1,
max = 10,
value = 2)
sliderInput("vthB9",
HTML("$$\\vartheta_b$$"),
min = 1,
max = 20,
value = 2)


Plot:

mForm9.1 <- as.formula("Y ~ vthB9 + th19*(x - thB9)")
mExpr9.1 <- mForm9.1[[3]]

output$Curve9 <- renderPlot({ th19 <- input$th19
vthB9 <- input$vthB9 thB9 <- input$thB9

eval(call("curve", mExpr9.1, col = 2, ylab = "", main =
expression(vartheta[b] + theta[1]*(x - theta[b]))))

},  height = 400, width = 600)

mainPanel(
tabsetPanel(type = "tabs",
tabPanel("Gráfico", plotOutput("Curve9"))
))


What happens here is that when 'x' is bigger than 'vthB9', the equation resumes itself to only 'vthB9', and this is only one of the cases I have. Anybody knows what to do?

*Hope I have been clear

*Im using
flexdashboard
, this is why the shiny might seen a little different

There are possibly multiple ways to plot a piecewise function in R. I am going to suggest probably the easiest way of doing it in this case:

We first define the piecewise function, say, fun

fun <- function(x) {
ifelse(test = x <= vthB9,
yes = vthB9 + th19 * (x - thB9),
no = vthB9)
}


which we then pass to curve

curve(expr = fun, from = 0, to = 10, col = 2, ylab = "",
main = expression(vartheta[b] + theta[1] * (x - theta[b])))


curve is going to input a vector as a parameter to the function fun. The usual if-else statements are not going to work because they can test only one value at a time - unless we write a for-loop or vectorise it somehow with a function Vectorize. Instead of that, we pick ifelse which is already vectorized.

Since you have used a shiny tag I've prepared a shiny app instead of flexdashboard :)

Full shiny example

  ui <- fluidPage(
sidebarLayout(
sidebarPanel(
sliderInput("th19",
HTML("&theta; <sub>1</sub>"),
min = 1,
max = 10,
value = 2),
sliderInput("thB9",
HTML("&theta; <sub>b</sub>"),
min = 1,
max = 10,
value = 2),
sliderInput("vthB9",
HTML("&thetasym; <sub>b</sub>"),
min = 1,
max = 20,
value = 2)
),
mainPanel(
tabsetPanel(type = "tabs",
tabPanel("Gráfico", plotOutput("Curve9")))
))
)

server <- function(input, output) {

output$Curve9 <- renderPlot({ th19 <- input$th19
vthB9 <- input$vthB9 thB9 <- input$thB9

# Define a piece wise function
fun <- function(x) {
ifelse(test = x <= vthB9,
yes = vthB9 + th19 * (x - thB9),
no = vthB9)
}
# x-axis goes now from 0 to 10
curve(expr = fun, from = 0, to = 10, col = 2, ylab = "",
main = expression(vartheta[b] + theta[1] * (x - theta[b])))

},  height = 400, width = 600)

}
shinyApp(ui, server)