app.css

.chart_container {
  position: relative;
  display: inline-block;
  font-family: Arial, Helvetica, sans-serif;
}
.rChart {
  display: inline-block;
  margin-left: 40px;
}
.yAxis {
  position: absolute;
  top: 0;
  bottom: 0;
  width: 40px;
}
.legend {
  position: absolute;
  top: 0;
  right: -160px;
  vertical-align: top;
}
.slider {
  margin-left: 40px;
  margin-top: 12px;
}

#text {
  position: relative;
  bottom: -35px;
  right: -65px;
}

server.R

require(shiny)
require(rCharts)

inputChoices <- c("A", "B", "C", "D")

shinyServer(function(input, output, session){
    
  	input2Choices <- reactive({
      inputChoices[-grep(input$input1, inputChoices)]
  	})

  	output$input1 <- renderUI({
  		selectInput("input1", "Input 1:", choices=as.list(inputChoices))
  	})

  	output$input2 <- renderUI({
  		if(is.null(input$input1))
  			return()
  		selectInput("input2", "Input 2:", choices=input2Choices())

  	})
  	
   dataInput1 <- reactive({
    if(is.null(input$input1))
      return()
    switch(input$input1,
           "A" = 1,
           "B" = 2,
           "C" = 3,
           "D" = 4)
    })

    dataInput2 <- reactive({
    if(is.null(input$input2))
      return()
    switch(input$input2,
           "A" = 1,
           "B" = 2,
           "C" = 3,
           "D" = 4)
    })

    getData <- function(){
      data1 <- dataInput1()
      data2 <- dataInput2()
      return(mtcars)
    }

    output$text <- renderTable({
      head(getData())
      })

  	output$show <- renderChart2({
       if(is.null(input$input1) | is.null(input$input2)){
        return(Rickshaw$new())
       }  
       if (input$input1 == input$input2){
        return(Rickshaw$new())
       }
       
        usp = reshape2::melt(USPersonalExpenditure)
        p4 <- Rickshaw$new()
        p4$layer(value ~ Var2, group = 'Var1', data = usp, type = 'line')
        p4$set(width = 600, slider = TRUE)
        p4$print("chart6")
        p4
    
  	})

})

ui.R

require(shiny)
require(rCharts)
shinyUI(pageWithSidebar(
  headerPanel("Dynamic UI inputs with Shiny"),
  sidebarPanel(
    includeCSS('app.css'),
    uiOutput('input1'),
    uiOutput('input2')
  ),
  mainPanel(
   showOutput("show", "rickshaw"),
   #verbatimTextOutput("show")
   tableOutput("text")
  )
))