use Perl

• scale linear then log (Score:0)

  by slanning (5049)

  Maybe I'm misunderstanding, but I think you want to first scale logarithmically: log($val) if it's log base 'e'. Then linearly: so find the max value in the logged sequence, then multiply each value by 255 and divide by the max. Here's a kind of generic script, if I got it right:

  #!/usr/bin/perl
  # convert @VALS to a log scale base $LOG_BASE
  # and scaled linearly to $SCALE_MAX
  
  use strict;
  use warnings;
  use List::Util qw(max);
  
  my $SCALE_MAX = 1000;
  my $LOG_BASE = 10;
  my @VALS = (1, 10, 100, 1000);
  
  main();
  
  sub main
  • Re: (Score:1)

    by veryrusty (8826)

    Need to scale linearly first in the case the minimum value is less than 1 before taking logs. (Also, $SCALE_MAX should be 255)

    Instead, if you simplify the mathematics (and you know the minimum and maximum values), calculate the logarithmic 'scaling factor'

    $scale = log( $maximum ) / 255;

    Then apply logarithmic scaling to each data element

    map { int( log( $_ - $minimum + 1 ) / $scale ) } @VALS;

    So that the minimum value scales to zero, maximum value scales to 255. Adjust the linear scale in the log calculatio
• Log2 for heatmap, fun with pack (Score:1)

  by n1vux (1492)

  i think both of the prior comments are on target.

  If you have such quantities of data that scaling and calling log repeatedly is a problem - and only if - there are old integer bitbang routines for log2 that could be done with XS or Inline::C or PDL.

  Or you could (ab)use Perl 5.10 pack() to grab the floating point representation's exponent

  Note that 256 buckets is a lot, hi res, for loglinear data unless it already was floating point or Math::BigFloat - as log2(MAXLONG) - log2(1) 256 or 8 bits -- it'

  --
  Bill
  # I had a sig when sigs were cool
  use Sig;