title: data.table() still converts strings to factors?
body: <p>From what I can see <a href="http://r-forge.r-project.org/tracker/?func=detail&amp;atid=978&amp;aid=1224&amp;group_id=240">here</a> I would assume that data.table v1.8.0+ does not automatically convert strings to factors.</p>
  
  <p>Specifically, to quote Matthew Dowle from that page: </p>
  
  <blockquote>
    <p>No need for stringsAsFactors. Done like this in v1.8.0 : o character columns are now allowed in keys and are preferred to factor. data.table() and setkey() no longer coerce character to factor. Factors are still supported.</p>
  </blockquote>
  
  <p>I'm not seeing that ... here's my R session transcript:</p>
  
  <p>First, I make sure I have a recent enough version of data.table > 1.8.0</p>
  
  <pre><code>&gt; library(data.table)
  data.table 1.8.8  For help type: help("data.table")
  </code></pre>
  
  <p>Next, I create a 2x2 data.table. Notice that it creates factors ...</p>
  
  <pre><code>&gt; m &lt;- matrix(letters[1:4], ncol=2)
  &gt; str(data.table(m))
  Classes ‘data.table’ and 'data.frame':  2 obs. of  2 variables:
   $ V1: Factor w/ 2 levels "a","b": 1 2
   $ V2: Factor w/ 2 levels "c","d": 1 2
   - attr(*, ".internal.selfref")=&lt;externalptr&gt; 
  </code></pre>
  
  <p>When I use stringsAsFactors in data.frame() and then call data.table(), all is well ...</p>
  
  <pre><code>&gt; str(data.table(data.frame(m, stringsAsFactors=FALSE)))
  Classes ‘data.table’ and 'data.frame':  2 obs. of  2 variables:
   $ X1: chr  "a" "b"
   $ X2: chr  "c" "d"
   - attr(*, ".internal.selfref")=&lt;externalptr&gt; 
  </code></pre>
  
  <p>What am I missing? Is data.frame() supposed to convert strings to factors, and if so, is there a "better way" of turning that behavior off?</p>
  
  <p>Thanks!</p>