title: Annotating numeric variable on a Leaflet map
body: <p>I made this plot</p>
  
  <p><img src="https://i.stack.imgur.com/5i8Q1.png" alt="enter image description here"></p>
  
  <p>With the following code.</p>
  
  <pre><code>library(XML)
  library(ggplot2)
  library(scales)
  library(plyr)
  library(maps)
  
  unemp &lt;-
    readHTMLTable('http://www.bls.gov/web/laus/laumstrk.htm',
                  colClasses = c('character', 'character', 'numeric'))[[2]]
  
  names(unemp) &lt;- c('rank', 'region', 'rate')
  unemp$region &lt;- tolower(unemp$region)
  
  us_state_map &lt;- map_data('state')
  map_data &lt;- merge(unemp, us_state_map, by = 'region')
  
  map_data &lt;- arrange(map_data, order)
  
  states &lt;- data.frame(state.center, state.abb)
  
  p1 &lt;- ggplot(data = map_data, aes(x = long, y = lat, group = group))
  p1 &lt;- p1 + geom_polygon(aes(fill = cut_number(rate, 5)))
  p1 &lt;- p1 + geom_path(colour = 'gray', linestyle = 2)
  p1 &lt;- p1 + scale_fill_brewer('Unemployment Rate (Jan 2011)', palette  = 'Set1')
  p1 &lt;- p1 + coord_map()
  p1 &lt;- p1 + geom_text(data = states, aes(x = x, y = y, label = state.abb, group = NULL), size = 2)
  p1 &lt;- p1 + theme_bw()
  p1
  </code></pre>
  
  <p>Now I want to reproduce the same plot with <code>leaflet</code> <code>R</code> package.</p>
  
  <pre><code>library(leaflet)
  
  leaflet(data = map_data) %&gt;% 
    setView(lng = -77.0167, lat = 38.8833, zoom = 4) %&gt;% 
    addTiles()
  </code></pre>
  
  <p>How can I annotate <code>rate</code> from <code>map_data</code> data.frame on the map with <code>leaflet</code> as <code>geom_polygon</code> did in <code>ggplot2</code> version?</p>