title: R data.table setkey with numeric column
body: <p>I'm using the data.table package in R. When trying to use setkey on a numeric column, I'm getting the following error message:</p>
  
  <pre><code>setkey(candidate.SNPs.MAF, p)
  
  Error in setkeyv(x, cols, verbose = verbose) :
  Column 'p' cannot be coerced to integer without losing fractional data.
  </code></pre>
  
  <p>I've seen a recent <a href="https://stackoverflow.com/questions/11157172/subset-and-recombine-dataframes-using-data-table-package-or-other-solutions-r"> answer</a> that suggests I need to have at least v1.8.1 and have confirmed that this problem occurs when using the newest version (1.8.2)</p>
  
  <pre><code>help(package="data.table")
                 Information on package 'data.table'
  
  Description:
  Package:            data.table
  Version:            1.8.2
  </code></pre>
  
  <p>Any suggestions?  I'd rather not have to revert to data.frames.</p>
  
  <p>My data structure looks like this:</p>
  
  <pre><code>str(can_SNPs_context)
  Classes 'data.table' and 'data.frame':  1031 obs. of  23 variables:
  $ Trait            : chr  "GH2_SLA" "GH2_SLA" "GH2_SLA" "GH2_SLA" ...
  $ Locus            : chr  "1" "1" "1" "1" ...
  $ Marker           : int  1825530 1844004 2251065 2444826 2832616 3557976 4299 650 4606939 4610965 6057450 ...
  $ p                : num  8.68e-08 7.21e-08 1.11e-07 1.20e-08 8.17e-08 ...
  </code></pre>
  
  <p>The p column is the one I'm trying to set as the key - do the very small values cause the problem?  </p>
  
  <p>R version 2.15.1 
  Linux x86_64</p>
  
  <p>Thanks!</p>