title: How to "melt" row wise instead of column wise in R?
body: <p>I have a data frame <code>A</code> that I would like to melt row wise instead of column wise to look like <code>B</code> (which also excludes observations with <code>NA</code> in them). Can this be accomplished with the "melt" function? </p>
  
  <pre><code>A &lt;- read.table(text="  Id1 Id2 Var1    Var2    Var3    
              1   1   1   2   NA  
              1   2   NA  3   4   
              1   3   5   6   7   ", header=T)
  
  
  B &lt;- read.table(text="  Id1 Id2 NewVar  
      1   1   1   
      1   1   2   
      1   2   3   
      1   2   4   
      1   3   5   
      1   3   6   
      1   3   7   ", header=T)
  </code></pre>
  
  <p>I found an <a href="https://stackoverflow.com/questions/19169820/row-wise-manipulation-on-large-dataset">answer</a> to a similar question but the function seems like overkill and is beyond my current R skills. </p>