title: How to sample 90/10 split% rows out of 2 columns
body: <p>I have the following data frame:</p>
  
  <pre><code>df &lt;- structure(list(Col1 = c(10L,14L,9L,42L,67L,3L,54L,93L,34L,22L), Col2 = c(20L,34L,29L,7L,11L,67L,84L,73L,35L,58L)), class = "data.frame", row.names = c(NA, -10L))
  </code></pre>
  
  <p>which looks like:</p>
  
  <pre><code>Col1 Col2
  10   20
  14   34
  9    29
  42   7
  67   11
  3    67
  54   84
  93   73
  34   35
  22   58
  </code></pre>
  
  <p>I want to append a new column <code>Col3</code> that samples 10% of row elements of <code>Col1</code> and 90% of row elements of <code>Col2</code>. So an acceptable output would look like the below:</p>
  
  <pre><code>df_new &lt;- structure(list(Col1 = c(10L,14L,9L,42L,67L,3L,54L,93L,34L,22L), 
                       Col2 = c(20L,34L,29L,7L,11L,67L,84L,73L,35L,58L),
                       Col3 = c(10L,14L,9L,7L,11L,67L,84L,73L,35L,58L)), class = "data.frame", row.names = c(NA, -10L))
  </code></pre>