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Often data is produced by one program, in the wrong format for later use by another program or person. In these situations another program can be written to parse and transform the original data into a format useful to the other. The term "Data Munging" is often used in programming circles for this task.

A request on the comp.lang.awk newsgroup led to a typical data munging task:

```
I have to analyse data files that have the following format:
Each row corresponds to 1 day and the field logic is: $1 is the date,
followed by 24 value/flag pairs, representing measurements at 01:00,
02:00 ... 24:00 of the respective day. In short:

<date> <val1> <flag1> <val2> <flag2> ...  <val24> <flag24>

Some test data is available at: 
... (nolonger available at original location)

I have to sum up the values (per day and only valid data, i.e. with
flag>0) in order to calculate the mean. That's not too difficult.
However, I also need to know what the "maximum data gap" is, i.e. the
longest period with successive invalid measurements (i.e values with
flag<=0)
```

The data is free to download and use and is of this format:

Data is no longer available at that link. Zipped mirror available here (offsite mirror).

```
1991-03-30	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1
1991-03-31	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	20.000	1	20.000	1	20.000	1	35.000	1	50.000	1	60.000	1	40.000	1	30.000	1	30.000	1	30.000	1	25.000	1	20.000	1	20.000	1	20.000	1	20.000	1	20.000	1	35.000	1
1991-03-31	40.000	1	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2
1991-04-01	0.000	-2	13.000	1	16.000	1	21.000	1	24.000	1	22.000	1	20.000	1	18.000	1	29.000	1	44.000	1	50.000	1	43.000	1	38.000	1	27.000	1	27.000	1	24.000	1	23.000	1	18.000	1	12.000	1	13.000	1	14.000	1	15.000	1	13.000	1	10.000	1
1991-04-02	8.000	1	9.000	1	11.000	1	12.000	1	12.000	1	12.000	1	27.000	1	26.000	1	27.000	1	33.000	1	32.000	1	31.000	1	29.000	1	31.000	1	25.000	1	25.000	1	24.000	1	21.000	1	17.000	1	14.000	1	15.000	1	12.000	1	12.000	1	10.000	1
1991-04-03	10.000	1	9.000	1	10.000	1	10.000	1	9.000	1	10.000	1	15.000	1	24.000	1	28.000	1	24.000	1	18.000	1	14.000	1	12.000	1	13.000	1	14.000	1	15.000	1	14.000	1	15.000	1	13.000	1	13.000	1	13.000	1	12.000	1	10.000	1	10.000	1

```

Only a sample of the data showing its format is given above. The full example file may be downloaded here.

Structure your program to show statistics for each line of the file, (similar to the original Python, Perl, and AWK examples below), followed by summary statistics for the file. When showing example output just show a few line statistics and the full end summary.
assistant
(formerly Perl 6)

```
my @gaps;
my $previous = 'valid';

for $*IN.lines -> $line { 
    my ($date, @readings) = split /\s+/, $line;
    my @valid;
    my $hour = 0;
    for @readings -> $reading, $flag {
        if $flag > 0 {    
            @valid.push($reading);
            if $previous eq 'invalid' {
                @gaps[*-1]{'end'} = "$date $hour:00";
                $previous = 'valid';
            }
        } 
        else
        {
            if $previous eq 'valid' {
                @gaps.push( {start => "$date $hour:00"} );
            }
            @gaps[*-1]{'count'}++;
            $previous = 'invalid';
        }
        $hour++;
    }
    say "$date: { ( +@valid ?? ( ( [+] @valid ) / +@valid ).fmt("%.3f") !! 0 ).fmt("%8s") }",
        " mean from { (+@valid).fmt("%2s") } valid."; 
};

my $longest = @gaps.sort({-$^a<count>})[0];

say "Longest period of invalid readings was {$longest<count>} hours,\n",
    "from {$longest<start>} till {$longest<end>}."

```

Output:

```
1990-01-01:   26.818 mean from 22 valid.
1990-01-02:   17.083 mean from 24 valid.
1990-01-03:   58.958 mean from 24 valid.
1990-01-04:   75.000 mean from 24 valid.
1990-01-05:   47.083 mean from 24 valid.
...
(many lines omitted)
...
2004-12-27:    2.483 mean from 23 valid.
2004-12-28:    3.383 mean from 23 valid.
2004-12-29:    2.448 mean from 23 valid.
2004-12-30:    2.839 mean from 23 valid.
2004-12-31:    2.057 mean from 23 valid.
Longest period of invalid readings was 589 hours,
from 1993-02-09 1:00 till 1993-03-05 14:00.

```