title: ERROR: invalid 'type' (list) of argument
body: <p>If i just run the leaflet part. it gives an ouput but in the shiny app it is giving the above error.</p>
  
  <p>When i try removing the code from addCircleMarkers it gives an out put without any marker. There is something wrong in that particular statement i am guessing.</p>
  
  <p>Also, I want to change the marker shape in leaflet for each of the type but that is again something not available from the resources i am finding over the internet. It shows that i have to manually find links (i will need almost 10 to do that)</p>
  
  <pre><code>data('zipcode')
  
  
  #removing the extra empty column
  data$X &lt;- NULL
  
  #cleaning the zipcodes
  data$ZIP.CODE &lt;- clean.zipcodes(data$ZIP.CODE)
  
  #adding the Stage2/Stage1 column
  combine$ratio &lt;- combine$Stage2/combine$Stage1
  combine &lt;- merge(data, zipcode,  by.x='ZIP.CODE', by.y='zip')
  combine[is.na(combine)] &lt;- 0
  
  
  ui&lt;-fluidPage(
    sidebarLayout(
      sidebarPanel(
        selectInput('rank','Ziprank',choices=levels(combine$ZIP.RANK),multiple=T,selected = 'A'),
        selectInput('type','Ziptype',choices=levels(combine$TYPE),multiple=T,selected = 'PUBLIC'),
        selectInput('market','Market',choices=c(1,2,3,4),multiple=T,selected = 1),
        selectInput('housevalue','Median Housing Value',choices=levels(combine$MEDIAN.HOUSING.VALUE),multiple=T,selected = '1HVL'),
        selectInput('familyincome','Median Family Value',choices=levels(combine$MEDIAN.FAMILY.INCOME),multiple=T,selected = '1MFI'),
        selectInput('buyingpower','Median House Buying Power',choices=levels(combine$MEDIAN.HOUSE.BUYING.POWER),multiple=T,selected = '1MHB'),
        selectInput('ethnicity','Ethnicity',choices=levels(combine$ETHNICITY),multiple=T,selected = '1ETH'),
        selectInput('population','Population Density',choices=levels(combine$POPULATION.DENSITY),multiple=T,selected = '1POP'),
        selectInput('masters','Masters Degree',choices=levels(combine$MASTERS.DEGREE),multiple=T,selected = '1MDG'),
        selectInput('associate','Associate Degree',choices=levels(combine$ASSOCIATES.DEGREE),multiple=T,selected = '1ADG'),
        selectInput('highschool','High School Age Population',choices=levels(combine$HIGH.SCHOOL.AGE.POPULATION),multiple=T,selected = '1HSP'),
        selectInput('epscode','EPS code',choices=levels(combine$EPS.CODE),multiple=T,selected = 'MS01'),
        selectInput('state','State',choices=unique(combine$state),multiple=T,selected = 'NY'),
        sliderInput('score','Zipscore', min(combine$ZIP.SCORE), max(combine$ZIP.SCORE), value=c(0.1,0.3))
      ),
      mainPanel(
        leafletOutput('plot')
      )
    )
  )
  server &lt;- function(input, output) {
    output$plot &lt;-renderLeaflet({
      final &lt;- subset(combine, ZIP.RANK %in% input$rank &amp;
                      TYPE %in% input$type &amp;
                      MARKET %in% input$market &amp;
                      MEDIAN.HOUSING.VALUE  %in% input$housevalue &amp;
                      MEDIAN.FAMILY.INCOME %in% input$familyincome &amp;
                      MEDIAN.HOUSE.BUYING.POWER %in% input$buyingpower &amp;
                      ETHNICITY %in% input$ethnicity &amp;
                      POPULATION.DENSITY %in% input$population &amp; 
                      MASTERS.DEGREE %in% input$masters &amp;
                      ASSOCIATES.DEGREE %in% input$associate &amp; 
                      HIGH.SCHOOL.AGE.POPULATION %in% input$highschool &amp;
                      EPS.CODE  %in% input$epscode &amp;
                      state %in% input$state &amp;
                      ZIP.SCORE &gt;= input$score[1] &amp; ZIP.SCORE &lt;= input$score[2]
                      )
      pal &lt;- colorNumeric(palette = "Reds", domain = c(0:1))
      p &lt;- final %&gt;%
        leaflet() %&gt;% 
        addProviderTiles('CartoDB') %&gt;%
        addCircleMarkers(data = final, color = ~pal(ZIP.SCORE),label=~GEONAME) %&gt;%
        addLegend(title = "ZipScore", pal = pal, values = c(0:1), 
                  position = "bottomright")
      p
    })
  }
  
  shinyApp(ui = ui, server = server)
  </code></pre>