title: how to x-y scatterplot two timeseries objects of unequal length, unequal frequency using ggplot2
body: <p>I have multiple time series objects covering different periods of time, with gaps in the data, and with varying frequencies (some hourly data, some 15-minute, some 1-minute).</p>
  
  <p>I'm trying to plot different time series objects against one another in x-y scatterplots - to see if there are obvious correlations, and make 'pretty' plots with ggplot for presentation. Obviously, one can only plot/compare data where it exists for <code>x</code> and <code>y</code> at the same time.</p>
  
  <p>I'm able to get a quick graphic with base graphics, but would like something more presentable.</p>
  
  <p>for example, this works in base R:</p>
  
  <pre><code>require(zoo)
  x &lt;- zoo(sort(rnorm(10)),as.POSIXct("2013/07/26")+1:10)
  y &lt;- zoo(sort(rnorm(30)),as.POSIXct("2013/07/26")+(1:30)/2)
  plot(x,y)
  </code></pre>
  
  <p>and trying to do the same with ggplot fails:</p>
  
  <pre><code>data &lt;- rbind(melt(fortify(x),id="Index"),melt(fortify(y),id="Index"))
  ggplot(data,aes(x=x,y=y))+geom_point()
  Don't know how to automatically pick scale for object of type zoo. Defaulting to continuous
  Don't know how to automatically pick scale for object of type zoo. Defaulting to continuous
  Error: Aesthetics must either be length one, or the same length as the dataProblems:x
  </code></pre>
  
  <p>suggestions on better titles/description are welcome</p>