<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html><body>
<p> </p>
<p>Hi,</p>
<p>data.table sorts double within machine tolerance :</p>
<pre>> sqrt(.Machine$double.eps)<br />[1] 1.490116e-08<br />> </pre>
<pre> </pre>
<pre>i.e. numbers closer than this are considered equal.</pre>
<pre> </pre>
<pre>Otherwise we wouldn't be able to do things like DT[.(3.14)].</pre>
<pre> </pre>
<pre>I had a quick look, see arguments of data.table:::ordernumtol which takes "tol" but there is no option provided (yet) to change this. Do we need one?</pre>
<pre> </pre>
<pre>In the examples section of one of the help pages it has an example which generates a series of numers very close together using pi. Note that your numbers are both close together, and, very close to 0.</pre>
<pre> </pre>
<pre>Matthew</pre>
<p> </p>
<p>On 30.04.2013 14:52, Arunkumar Srinivasan wrote:</p>
<blockquote type="cite" style="padding-left:5px; border-left:#1010ff 2px solid; margin-left:5px; width:100%"><!-- html ignored --><!-- head ignored --><!-- meta ignored -->
<div>Hi there,</div>
<div>I just saw something strange when I was sorting a column of p-values. I checked the data.table bug tracker for words "sort" and "floating point" and there were no hits for this case. There's a bug for "integer 64" sort on a column though.</div>
<div>So, here's a reproducible example. I'd be glad to file a bug, if it is and be corrected if it's something I am doing wrong.</div>
<div>
<div>set.seed(45)</div>
<div>dt <- data.table(x=sample(50), y= sample(c(seq(0, 1, length.out=1000), 7000000:7000100), 50)/1e7)</div>
<div>head(dt)</div>
<div> x y</div>
<div>1: 32 5.395395e-08</div>
<div>2: 16 6.956957e-08</div>
<div>3: 12 2.142142e-08</div>
<div>4: 18 5.855856e-08</div>
<div>5: 17 6.216216e-08</div>
<div>6: 14 5.025025e-08</div>
<div>setkey(dt, "y") # sort by column y</div>
<div>head(dt, 10)</div>
<div> x y</div>
<div> 1: 47 1.401401e-09</div>
<div> 2: 12 2.142142e-08</div>
<div> 3: 24 1.391391e-08</div>
<div> 4: 43 9.809810e-09 <~~~ obviously false</div>
<div> 5: 1 2.932933e-08</div>
<div> 6: 48 2.562563e-08</div>
<div> 7: 49 1.891892e-08</div>
<div> 8: 40 2.182182e-08</div>
<div> 9: 9 7.307307e-09 <~~~ obviously false</div>
<div>10: 45 2.482482e-08</div>
</div>
<div>
<div>Best,</div>
<div>Arun</div>
</div>
</blockquote>
<p> </p>
<div> </div>
</body></html>