title: stl() decomposition won't accept univariate ts object?
body: <p>I'm have issues with stl() time series decomposition function in R telling me my ts object is not univariate when it actually is?</p>
  
  <pre><code>tsData &lt;- ts(data = dummyData, start = c(2012,1), end = c(2014,12), frequency = 12)
  
  &gt; tsData
       Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
  2012  22  26  34  33  40  39  39  45  50  58  64  78
  2013  51  60  80  80  93 100  96 108 111 119 140 164
  2014 103 112 154 135 156 170 146 156 166 176 193 204
  
  &gt; class(tsData)
  [1] "ts"
  
  &gt; stl(tsData, s.window = "periodic")
  Error in stl(tsData, s.window = "periodic") : 
    only univariate series are allowed
  
  &gt; dput(dummyData)
  structure(list(index = c(22L, 26L, 34L, 33L, 40L, 39L, 39L, 45L, 
  50L, 58L, 64L, 78L, 51L, 60L, 80L, 80L, 93L, 100L, 96L, 108L, 
  111L, 119L, 140L, 164L, 103L, 112L, 154L, 135L, 156L, 170L, 146L, 
  156L, 166L, 176L, 193L, 204L)), .Names = "index", class = "data.frame", row.names = c(NA, 
  -36L))
  </code></pre>
  
  <p>Anyone know how to fix this issue?</p>