The N50 contig size is a weighted median value and defined as
the length of the smallest contig S in the sorted list of all
contigs where the cumulative length from the largest contig to
contig S is at least 50% of the total length.
 

 

perl -e 'my ($len,$total)=(0,0);my @x;while(<>){if(/^[\>\@]/){if($len>0){$total+=$len;push@x,$len;};$len=0;}else{s/\s//g;$len+=length($_);}}if ($len>0){$total+=$len;push @x,$len;}@x=sort{$b<=>$a}@x; my ($count,$half)=(0,0);for (my $j=0;$j<@x;$j++){$count+=$x[$j];if(($count>=$total/2)&&($half==0)){print "N50: $x[$j]\n";$half=$x[$j]}elsif($count>=$total*0.9){print "N90: $x[$j]\n";exit;}}'  contigs.fahttp://seqanswers.com/forums/showthread.php?t=2766

 

 

http://seqanswers.com/forums/showthread.php?t=2766