title: Split data frame by values in a column
body: <p>I'm trying to find a general way to split a table by unique value in a column and assign them to different varibles .I have a table like this</p>
  
  <pre><code>&gt; x &lt;-expand.grid(c("a","b","c"), c(1:2),c(1:2))
  &gt; x
  Var1 Var2 Var3
  1     a    1    1
  2     b    1    1
  3     c    1    1
  4     a    2    1
  5     b    2    1
  6     c    2    1
  7     a    1    2
  8     b    1    2
  9     c    1    2
  10    a    2    2
  11    b    2    2
  12    c    2    2    
  </code></pre>
  
  <p>What i need is something like </p>
  
  <pre><code>&gt; xa &lt;- x[x$Var1 == "a",]
  &gt; xb &lt;- x[x$Var1 == "b",]
  &gt; xc &lt;- x[x$Var1 == "c",]
  &gt; xa
  Var1 Var2 Var3
  1     a    1    1
  4     a    2    1
  7     a    1    2
  10    a    2    2
  &gt; xb
  Var1 Var2 Var3
  2     b    1    1
  5     b    2    1
  8     b    1    2
  11    b    2    2
  &gt; xc
  Var1 Var2 Var3
  3     c    1    1
  6     c    2    1
  9     c    1    2
  12    c    2    2
  </code></pre>
  
  <p>But how can I do this in one command assuming I don't know the values and number of unique values in Var1? </p>
  
  <p>Thanks</p>