title: R return the index of the minimum column for each row
body: <p>I have a data.frame that contains 4 columns (given below). I want to find the index of the minimum column (NOT THE VALUE) for each row. Any idea hiw to achieve that? </p>
  
  <pre><code>&gt; d
              V1         V2         V3         V4
  1  0.388116155 0.98999967 0.41548536 0.76093748
  2  0.495971331 0.47173142 0.51582728 0.06789924
  3  0.436495321 0.48699268 0.21187838 0.54139290
  4  0.313514389 0.50265539 0.08054103 0.46019601
  5  0.277275961 0.39055360 0.29594162 0.70622532
  6  0.264804739 0.86996266 0.85708635 0.61136741
  7  0.627344463 0.54277873 0.96769568 0.80399490
  8  0.814420492 0.35362949 0.39023446 0.39246250
  9  0.517459983 0.65895805 0.93662382 0.06762166
  10 0.498319937 0.67081260 0.43225997 0.42139151
  11 0.046862110 0.97304915 0.06542971 0.09779383
  12 0.619009734 0.82363618 0.14514799 0.52858058
  13 0.007262782 0.82203403 0.08573499 0.61094206
  14 0.001602586 0.33241230 0.57762669 0.45285004
  15 0.698388370 0.83541257 0.21051568 0.84431347
  16 0.296088411 0.34363164 0.02179999 0.70551493
  17 0.897869571 0.50625928 0.92861583 0.61249019
  18 0.372497428 0.29025182 0.23201891 0.55737699
  19 0.172931860 0.03604668 0.50291560 0.10850847
  20 0.988827604 0.15800337 0.87999839 0.09899663
  </code></pre>
  
  <p>So I want the following output:</p>
  
  <pre><code>1    1
  2    4
  3    3
  4    3
  </code></pre>
  
  <p>which continues for all the rows.
  Thanks</p>