title: Format of time series data with regression variables
body: <p>I am new to R and am attempting an analysis in R with the tslm() function.</p>
  
  <p>Sample data in csv format:</p>
  
  <pre><code>    UnitSales   GDP GDPPerCap   CPI PropInvIndex    DispIncTopDecile    TransCommSecDecile  CivilVehOwn Urban   AutoFin
  2000    1   1198243.4   949 81.62   4984    10643   618 1609    36.22   0
  2001    2   1324337.8   1042    81.38   6344    14219   782 1802    37.66   0
  2002    3   1453827.558 1135    80.8    7790.9223   18995.9 991.2   2053.17 39.08978381 0
  2003    4   1640958.735 1274    81.83   10153.8009  21837.3 1106    2382.93 40.53022975 0
  2004    5   1931644.33  1409    85.02   13158.2516  25377.2 1274.2  2693.71 41.76000862 0
  2005    6   2256902.591 1731    86.56   15909.2471  28773.1 1590.3  3160    42.98999663 0
  2006    7   2712950.885 2069    87.83   19422.9174  31967.3 1801    3697.3531   44.34301016 0
  2007    9   3494055.942 2651    92.02   25288.8373  36784.5 2467.7  4358.355    45.8892446  0.1
  2008    11  4521827.271 3414    97.45   31203.1942  43613.8 2632.9  5099.6094   46.98950317 0.12
  2009    13  4990233.519 3749    96.76   36241.808   46826.1 3181.9  6280.6086   48.34170101 0.14
  2010    15  5930502.27  4433    100 48259.403   51431.6 3630.6  7801.8259   49.94966105 0.16
  2011    18  7321891.955 5447    105.45  61796.8858  58841.9 3963    9356.3163   51.27027127 0.18
  2012    21  8229490.03  6093    108.22  71803.7869  63824.2 4304.1  10933.0912  52.57008656 0.22
  </code></pre>
  
  <p>I load the data and then attempt to run:</p>
  
  <pre><code>testc &lt;- tslm(UnitSales~GPD+trend, data=lm0015c)
  </code></pre>
  
  <p>A simple attempt to model UnitSales from the GDP variable plus the trend. </p>
  
  <p>I get the following error:</p>
  
  <pre><code>Error in tslm(UnitSales ~ GPD + trend, data = lm0015c) : 
    Not time series data
  </code></pre>
  
  <p>How do I designate the data as a time series?</p>