# GMCH....

my @funcs_gmch = (
    undef,  # first_timestamp
    \&avg_gmch,
    \&max_gmch,
    \&min_gmch,
    \&first_gmch,
    \&last_gmch,
  ) ;

sub downsample_gmch {
    my( $resolution, $data ) = @_;

    my $first_timestamp =
        first_timestamp_for_resolution( $resolution, $data->[0][0] );

    my @output;
    push( @output, $first_timestamp );

    push( @output, $funcs_gmch[$_]->( $data, $_ ) ) for ( 1..$#funcs_gmch);

    return( @output );
}

sub avg_gmch {
  my ($rd, $i) = @_ ;

  my $s = 0 ;
  $s += $_->[$i] foreach (@$rd) ;

  return $s / scalar(@$rd) ;
} ;

sub max_gmch {
  my ($rd, $i) = @_ ;

  my $m = $rd->[0]->[$i] ;
  $m < $_->[$i] and $m = $_->[$i]  foreach (@$rd) ;

  return $m ;
} ;

sub min_gmch {
  my ($rd, $i) = @_ ;

  my $m = $rd->[0]->[$i] ;
  $m > $_->[$i] and $m = $_->[$i]  foreach (@$rd) ;

  return $m ;
} ;

sub first_gmch {
  my ($rd, $i) = @_ ;

  return $rd->[0]->[$i] ;
} ;

sub last_gmch {
  my ($rd, $i) = @_ ;

  return $rd->[-1]->[$i] ;
} ;