title: univariate time series into training and test splitting in R
body: <p>I want to split the univariate time series (14139 observations) into training and test set for 60% and 40% respectively. I enter the command<br>
      <code>splits (APILts, c(rep("train", 8483), "test"))</code>
  then R resulted:
      <code>Error: is.timeSeries(x) is not TRUE</code></p>