title: Reshape wide data to long format
body: <p>I am facing trouble reshaping my wide data into a long format using <code>reshape</code> <code>melt</code>.But I couldn't find a solution best suited to my need. Sorry if I am duplicating this question. My monthly data (CSV file)of a single variable is in the following format;</p>
  <pre><code>Date        level1  level2  level3  level4 ..... level100
  1/1/2003    191.3    191.4  191.4   191.4
  1/2/2003    184.3    184.3  184.3   184.3
  1/3/2003    176.5    176.5  176.5   176.5
  1/4/2003    175.5    175.5  175.5   175.5
  ..
  ..
  1/12/2003
  </code></pre>
  <p>I am trying to reshape in this format</p>
  <pre><code>Date        Level   value
  1/1/2003    1       191.3
  1/1/2003    2       191.4
  ..      ..      ..
  1/1/2003    100     #value
  1/2/2003    1       #value
  1/2/2003    2       #value
  ..
  1/2/2003    100     #value
  </code></pre>
  <p>and so on...</p>