in reply to Filling in missing values in an array

The solution below uses the flip-flop operator to see if we are in a NULL section or not. If we just started seeing NULL's that array index is noted. When we have seen the first number past the NULL's, a sub is called to go back fill the correct numbers into the array. 
#!/usr/bin/perl -w
use strict;

my $data = '4 NULL NULL NULL 5 1 NULL NULL 2 NULL 6';

my @data = split(/\s+/,$data);

my $iFirstNULL;
my $cur_index=0;

foreach (@data)
{
   if (my $num = /NULL/.../\d/)
   {
     $iFirstNULL = $cur_index if $num == 1;
     insertValues($iFirstNULL-1,$cur_index,\@data) if $num =~ /E0/;
   }
   $cur_index++;
}

print "@data"; #prints 4 4 4.5 5 5 1 1 2 2 4 6

sub insertValues
{
   my ($istart, $iend, $aref) = @_;
   my $pos = $istart+1;
   
   my $beginNum = $aref->[$istart];
   my $endNum   = $aref->[$iend];

   while ($aref->[$pos] eq 'NULL')
   {
      if ($pos-$istart < $iend-$pos)   # closer to start
      {
         $aref->[$pos] = $beginNum;
      }
      elsif($pos-$istart > $iend-$pos) # closer to end
      {
         $aref->[$pos] = $endNum;
      }
      else                             # directly in middle
      {
         $aref->[$pos] = ($endNum + $beginNum)/2;
      }
      $pos++;
   }
}

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Re^2: Filling in missing values in an array
by roboticus (Chancellor) on Jun 29, 2011 at 12:35 UTC

    Marshall:

    I was toying with splice and made an amusing variation:

    #!/usr/bin/perl -w
use strict;

my $data = '4 NULL NULL NULL 5 1 NULL NULL 2 NULL 6';

my @data = split(/\s+/,$data);

my $iFirstNULL;
my $cur_index=0;

foreach (@data)
{
   if (my $num = /NULL/.../\d/)
   {
     $iFirstNULL = $cur_index if $num == 1;
     splice @data, $iFirstNULL, $cur_index-$iFirstNULL,
                   newVals(@data[$iFirstNULL-1 .. $cur_index])
       if $num =~ /EO/;
   }
   $cur_index++;
}

print "@data\n"; #prints 4 4 4.5 5 5 1 1 2 2 4 6

sub newVals {
    my ($leftVal, $rightVal, $num) = ($_[0], $_[-1], scalar(@_)-2);

    # Left half of the return list is $leftVal, right half is $rightVa
+l
    my @ret = (($leftVal) x int($num/2), ($rightVal) x int($num/2));

    # Insert the average in the center for an odd-sized number of null
+s
    splice @ret, int($num/2), 0, ($leftVal+$rightVal)/2 if $num&1;

    return @ret;
}

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    ...roboticus

    When your only tool is a hammer, all problems look like your thumb.

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