title: Row to column with identifier
body: <p>Im trying to convert the following data</p>
  <pre><code>sub-control01 0.0787704 0.0361882 -0.0249416
  sub-control02 0.0901315 NaN NaN
  sub-control03 -0.150466 -0.0306896 NaN
  sub-control04 -0.0807549 -0.105495 -0.0603963
  sub-control05 -0.12861 -0.13731 NaN
  </code></pre>
  <p>into something like</p>
  <pre><code>sub-control01 0.0787704
  sub-control01 0.0361882
  sub-control01 -0.0249416
  sub-control02 0.0901315
  sub-control02 NaN
  sub-control02 NaN
  sub-control03 -0.150466
  sub-control03 -0.0306896
  sub-control03 NaN
  sub-control04 -0.0807549
  sub-control04 -0.105495
  sub-control04 -0.0603963
  sub-control05 -0.12861
  sub-control05 -0.13731
  sub-control05 NaN
  </code></pre>
  <p>So far, I can only make it look like this using tr -s ' ' '\n' &lt; file1.txt &gt; file2.txt</p>
  <pre><code>sub-control01
  0.0787704
  0.0361882
  -0.0249416
  sub-control02
  0.0901315
  NaN
  NaN
  sub-control03
  -0.150466
  -0.0306896
  NaN
  sub-control04
  -0.0807549
  -0.105495
  -0.0603963
  sub-control05
  -0.12861
  -0.13731
  NaN
  </code></pre>
  <p>Any suggestions?
  Thanks!</p>