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<p class=MsoNormal>I have a 2-dimensional Numeric array with the shape (2,N)
and I want to remove all duplicate rows from the array. For example if I start
out with:<o:p></o:p></p>
<p class=MsoNormal>[[1,2],<o:p></o:p></p>
<p class=MsoNormal>[1,3],<o:p></o:p></p>
<p class=MsoNormal>[1,2],<o:p></o:p></p>
<p class=MsoNormal>[2,3]]<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I want to end up with<o:p></o:p></p>
<p class=MsoNormal>[[1,2],<o:p></o:p></p>
<p class=MsoNormal>[1,3],<o:p></o:p></p>
<p class=MsoNormal>[2,3]].<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>(Order of the rows doesn’t matter, although order of
the two elements in each row does.)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The problem is that I can’t find any way of doing this
that is efficient with large data sets (in the data set I am using, N > 1000000)<o:p></o:p></p>
<p class=MsoNormal>The normal method of removing duplicates by putting the
elements into a dictionary and then reading off the keys doesn’t work
directly because the keys – rows of Python arrays – aren’t
hashable.<o:p></o:p></p>
<p class=MsoNormal>The best I have been able to do so far is:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>def remove_duplicates(x):<o:p></o:p></p>
<p class=MsoNormal> d
= {}<o:p></o:p></p>
<p class=MsoNormal> for
(a,b) in x:<o:p></o:p></p>
<p class=MsoNormal> d[(a,b)]
= (a,b)<o:p></o:p></p>
<p class=MsoNormal> return
array(x.values())<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>According to the profiler the loop takes about 7 seconds and
the call to array() 10 seconds with N=1,700,000.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Is there a faster way to do this using Numeric?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>-Alex Mont<o:p></o:p></p>
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