title: Adding if statements for checkboxGroupInput in Shiny
body: <p>I'm having issues adding a checkboxes in a shiny app. I want to be able to check  to add either a linear regression line, loess, or none at all. This is using the diamond data. 
  Any help would be greatly appreciated:</p>
  
  <p><strong>ui.R</strong></p>
  
  <pre><code>library(shiny)
  shinyUI(fluidPage(
  fluidRow(
  sidebarLayout(
    sidebarPanel(
      numericInput("size","Size",value=1,min=0,max=1,step=0.1),
      sliderInput("opaqueness","Opaqueness",0,min=0,max=1),
      checkboxInput("color","Color",value=T),
      checkboxGroupInput("lines","Lines",choices=c("lm","loess"))
      #add inputs
  
      ),
    mainPanel(
      plotOutput("diamondgraph")
    )
  )
  )
  ))
  </code></pre>
  
  <p><strong>server.R</strong></p>
  
  <pre><code>library(dplyr)
  library(ggplot2)
  library(shiny)
  data&lt;-diamonds
  data&lt;-filter(data,color=="E"|color=="I"|color=="J")
  
  
  shinyServer(function(input, output) {
    output$diamondgraph&lt;-renderPlot({
  g&lt;-ggplot(data=data,aes(x=carat,y=price))
  if (input$color){
    gcol&lt;-g+geom_point(aes(color=color),alpha=input$opaqueness,size=input$size)+scale_x_log10()+
      ggtitle("Scatterplot of Carat vs Price")
  
  }else{
    gcol&lt;-g+geom_point(alpha=input$opaqueness, size=input$size)+
      geom_smooth()+
      scale_x_log10()+
      ggtitle("Scatterplot of Carat vs Price")
  }
  if (input$lines =="lm"){
    gcol&lt;-g+geom_point(aes(color=color),alpha=input$opaqueness,size=input$size)+geom_smooth(aes(color=color, method=lm))+scale_x_log10()+
      ggtitle("Scatterplot of Carat vs Price")
  }
  if 
  (input$lines == "loess"){
    gcol&lt;-g+geom_point(aes(color=color),alpha=input$opaqueness,size=input$size)+geom_smooth(aes(color=color)) + scale_x_log10()+
      ggtitle("Scatterplot of Carat vs Price")
  } else 
    gcol&lt;-g+geom_point(aes(color=color),alpha=input$opaqueness,size=input$size) + scale_x_log10()+
      ggtitle("Scatterplot of Carat vs Price")
  gcol
     })
  
  })
  </code></pre>