title: Concatenate a vector to a dataframe
body: <p>I am trying to concatenate a vector (let's call it y) of length N x 1 to a matrix (let's call it x) of length N x N. Each value in x needs to be concatenated to the corresponding row, determined by that value's position in x. I am looking for a vectorized answer that does not rely on a loop. To illustrate:</p>
  
  <pre><code>x &lt;- as.data.frame(matrix(1:100,nrow=10,ncol=10))
  y &lt;- c(1:10)
  
  for(k in c(1:(ncol(x)))){
  x[k,] &lt;- paste0(y[k],x[k,])
  }
  
  V1   V2   V3   V4   V5   V6   V7   V8   V9   V10
  11  111  121  131  141  151  161  171  181   191
  22  212  222  232  242  252  262  272  282   292
  33  313  323  333  343  353  363  373  383   393
  44  414  424  434  444  454  464  474  484   494
  55  515  525  535  545  555  565  575  585   595
  66  616  626  636  646  656  666  676  686   696
  77  717  727  737  747  757  767  777  787   797
  88  818  828  838  848  858  868  878  888   898
  99  919  929  939  949  959  969  979  989   999
  1010 1020 1030 1040 1050 1060 1070 1080 1090 10100
  </code></pre>