while (){ s/^\s+|\s+//g; if(length($_)<1){ next;} @f=split(/,/,$_); push(@col1,{TIME=>$f[0],GOOD=>$f[1]}); push(@col2,{TIME=>$f[0],GOOD=>$f[2]}); if($unique{$f[0]}!=1){ push(@times,$f[0]); $unique{$f[0]}=1; } } # reverse sort by col1 values to backfill # forward sort by col1 time to catch last good foreach(sort {$$b{GOOD}<=>$$a{GOOD} || $$a{TIME}<=>$$b{TIME}} @col1){ if( ($$_{TIME}<$last_time) && ($$_{GOOD} == -999.9) ) { $out1{$$_{TIME}}=$last_good; }elsif($$_{GOOD} == -999.9){ $out1{$$_{TIME}}=$last_good; }else{ $last_time=$$_{TIME}; $last_good=$$_{GOOD}; $out1{$$_{TIME}}=$$_{GOOD}; } } foreach(sort {$$b{GOOD}<=>$$a{GOOD} && $$a{TIME}<=>$$b{TIME}} @col2){ if( ($$_{TIME}<$last_time) && ($$_{GOOD} == -999.9) ) { $out2{$$_{TIME}}=$last_good; }elsif($$_{GOOD} == -999.9){ $out2{$$_{TIME}}=$last_good; }else{ $last_time=$$_{TIME}; $last_good=$$_{GOOD}; $out2{$$_{TIME}}=$$_{GOOD}; } } foreach $time (@times){ print "$time,$out1{$time},$out2{$time}\n"; } # time,col1,col2 # (-999.9 out-of-range to indicate missing # and distinguish from true zeroes) __DATA__ 0.01,-999.9,1 0.02,-999.9,-999.9 0.03,-999.9,3 0.04,2,-999.9 0.05,-999.9,-999.9 0.06,5,4 #### # time,col1,col2 0.01,2,1 0.02,2,1 0.03,2,3 0.04,2,1 0.05,2,1 0.06,5,4