title: Mean and SD in R
body: <p>maybe it is a very easy question. This is my data.frame:</p>
  
  <pre><code>&gt; read.table("text.txt")
     V1       V2
  1  26    22516
  2  28    17129
  3  30    38470
  4  32    12920
  5  34    30835
  6  36    36244
  7  38    24482
  8  40    67482
  9  42    23121
  10 44    51643
  11 46    61064
  12 48    37678
  13 50    98817
  14 52    31741
  15 54    74672
  16 56    85648
  17 58    53813
  18 60   135534
  19 62    46621
  20 64    89266
  21 66    99818
  22 68    60071
  23 70   168558
  24 72    67059
  25 74   194730
  26 76   278473
  27 78   217860
  </code></pre>
  
  <p>It means that I have 22516 sequences with length 26, 17129 sequences with length 28, etc. I would like to know the sequence length mean and its standard deviation. I know how to do it, but I know to do it creating a list full of 26 repeated 22516 times and so on... and then compute the mean and SD. However, I thing there is a easier method. Any idea?</p>
  
  <p>Thanks.</p>