An example using a SelectInput element in Shiny to render a plot. Using a sidebar layout and the 'WorldPhones' dataset.

server.R

library(shiny)

# Rely on the 'WorldPhones' dataset in the datasets
# package (which generally comes preloaded).
library(datasets)

# Define a server for the Shiny app
shinyServer(function(input, output) {
  
  # Fill in the spot we created for a plot
  output$phonePlot <- renderPlot({
    
    # Render a barplot
    barplot(WorldPhones[,input$region]*1000, 
            main=input$region,
            ylab="Number of Telephones",
            xlab="Year")
  })
})

ui.R

library(shiny)

# Rely on the 'WorldPhones' dataset in the datasets
# package (which generally comes preloaded).
library(datasets)

# Define the overall UI
shinyUI(
  
  # Use a fluid Bootstrap layout
  fluidPage(    
    
    # Give the page a title
    titlePanel("Telephones Around the World"),
    
    # Generate a row with a sidebar
    sidebarLayout(      
      
      # Define the sidebar with one input
      sidebarPanel(
        selectInput("region", "Region:", 
                    choices=colnames(WorldPhones)),
        hr(),
        helpText("Data from AT&T (1961) The World's Telephones.")
      ),
      
      # Create a spot for the barplot
      mainPanel(
        plotOutput("phonePlot")  
      )
      
    )
  )
)

After running above code I got an error:'height' must be a vector or a matrix.
Would you help me solve this error??