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my @l1=("Date","IndexID","Maturity","OnTheRun","CompositePrice","Compo
+siteSpread","ModelPrice","ModelSpread","Depth","Heat");
my @l2=("OnTheRun","CompositePrice","CompositeSpread","Depth");

foreach my $f (@l1){
        if (join(",",@l2) !~ /\b$f\b/){
          $f='null';
        }
      }

my @l3= map {(join(",",@l2) =~ /\b$f\b/)?$f:"null"} @l1;

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