title: geom_point runs from console but not from R Markdown (knit html)
body: <p>I have the following dataset</p>
  
  <pre><code>head(myDataFrame)
    rating      lat       lon
  1    4.0 40.70952 -74.01460
  2    3.8 40.70144 -74.01514
  3    4.1 40.72795 -74.00139
  4    4.1 40.71792 -73.99012
  5    4.1 40.72706 -73.98855
  6    4.1 40.71568 -74.00849
  </code></pre>
  
  <p>and the following point</p>
  
  <pre><code>geo
  [1] "40.7127837"        "-74.0059413"       "New York, NY, USA"
  </code></pre>
  
  <p>When I run the following function from the console it runs great  </p>
  
  <pre><code>showLocationsOnMap &lt;- function(geo,myDataFrame) {
    map &lt;- get_map(location = c( lon =as.numeric(geo[2]), lat = as.numeric(geo[1])), maptype = "satellite", zoom = 14)
    ggmap(map) + geom_point(data = myDataFrame, aes(x=lon, y=lat, color=rating)) + scale_colour_gradientn(colours=rainbow(4))
  }
  </code></pre>
  
  <p>but when I run it from the R Markdown I get the following error</p>
  
  <blockquote>
    <p>Error: ggplot2 doesn't know how to deal with data of class numeric In addition: Warning messages: 1: package 'RCurl' was built under R version 3.2.4 2: package 'ggplot2' was built under R version 3.2.4 Execution halted </p>
  </blockquote>