title: When I read in a large table using fread it slightly changes the numbers in one of the columns
body: <p>I have a large file that looks like this</p>
  
  <pre><code>region              type    coeff      p-value  distance    count
  82365593523656436   A      -0.9494     0.050    -16479472.5 8
  82365593523656436   B      0.47303     0.526    57815363.0  8
  82365593523656436   C      -0.8938     0.106    42848210.5  8
  </code></pre>
  
  <p>When I read it in using fread, suddenly 82365593523656436 is not found anymore</p>
  
  <pre><code>correlations &lt;- data.frame(fread('all_to_all_correlations.txt'))
  &gt; "82365593523656436" %in% correlations$region
  [1] FALSE
  </code></pre>
  
  <p>I can find a slightly different number</p>
  
  <pre><code>&gt; "82365593523656432" %in% correlations$region
  [1] TRUE
  </code></pre>
  
  <p>but this number is not in the actual file</p>
  
  <pre><code>grep 82365593523656432 all_to_all_correlations.txt 
  </code></pre>
  
  <p>gives no results, while</p>
  
  <pre><code>grep 82365593523656436 all_to_all_correlations.txt 
  </code></pre>
  
  <p>does.</p>
  
  <p>When I try to read in the small sample file I showed above instead of the full file I get</p>
  
  <pre><code>Warning message:
  In fread("test.txt") :
    Some columns have been read as type 'integer64' but package bit64 isn't  loaded. 
  Those columns will display as strange looking floating point data. 
  There is no need to reload the data. 
  Just require(bit64) toobtain the integer64 print method and print the data again.
  </code></pre>
  
  <p>and the data looks like</p>
  
  <pre><code>     region type    coeff       p.value  distance      count
  1 3.758823e-303    A -0.94940   0.050    -16479472     8
  2 3.758823e-303    B  0.47303   0.526     57815363     8
  3 3.758823e-303    C -0.89380   0.106     42848210     8
  </code></pre>
  
  <p>So I think during reading 82365593523656436 was changed into 82365593523656432. How can I prevent this from happening?</p>