title: Pass subset argument through a function to subset
body: <p>I would like to have a function which calls <code>subset</code>, and passes on a <code>subset</code> argument:</p>
  
  <pre><code>df &lt;- data.frame(abc=c("A","A","B","B"),value=1:4)
  subset(df,abc=="A")
  ## works of course:
  #  abc value
  #1   A     1
  #2   A     2
  
  mysubset &lt;- function(df,ssubset)
    subset(df,ssubset)
  
  mysubset(df,abc=="A")
  ## Throws an error
  # Error in eval(expr, envir, enclos) : object 'abc' not found
  
  mysubset2 &lt;- function(df,ssubset)
    subset(df,eval(ssubset))
  
  mysubset2(df,expression(abc=="A"))
  ## Works, but needs expression
  </code></pre>
  
  <p>I tried with <code>substitute</code>, but was not able to find the right combination. How can I get this working?</p>