Null values in Perl Calculation

PaulB-Liverpool has asked for the wisdom of the Perl Monks concerning the following question:

Hi. New poster here! I'm building a Cricket Sports Database. The code below runs fine until it gets past batters who have scored runs, (returns 236 records) but when it hits bowlers with no runs (blank Field), I get Division by Zero error. I've tried allsorts of solutions ... mainly from here; but I'm a bit new and can't figure it out... It's a flat file system DBMan from years ago; but still great if working!! I've truncated the table for easier viewing...


sub html_record {
# --------------------------------------------------------
my (%rec) = @_;        # Load any defaults to put in the VALUE field.
    
$total = 0;
$total = $rec{'BatterRuns'} + $rec{'HighestScore'};

$baverage1 = 0;
$baverage1 = $rec{'Innings'} - $rec{'NotOut'};
    
$baverage = 0;
$baverage =  $rec{'BatterRuns'} / $baverage1;    

# Gives 236 correct results until it hits a blank bowler field 
# who has not batted ie: NULL</b>
    
($db_auto_generate and print &build_html_record(%rec) and return);
  
   
print qq|
   
<TABLE WIDTH="450" CELLPADDING=0 CELLSPACING=0 BORDER=1 BGCOLOR="#FFFF
+CC">
<TR><TD ALIGN="Right" VALIGN="TOP"><$font_color>Batting Average:</FONT
+></TD><TD>&nbsp;<$font>$baverage</Font></TD></TR>

</TABLE>
|;

}
[download]

Comment on Null values in Perl Calculation Download Code

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Re: Null values in Perl Calculation by tybalt89 (Monsignor) on May 02, 2024 at 23:50 UTC
Try changing `$baverage = $rec{'BatterRuns'} / $baverage1;` [download] to `$baverage1 and $baverage = $rec{'BatterRuns'} / $baverage1;` [download] This should only do the divide when $baverage1 is non-zero (i.e. true).	[reply] [d/l] [select]
Re: Null values in Perl Calculation by syphilis (Archbishop) on May 03, 2024 at 00:44 UTC
... but when it hits bowlers with no runs (blank Field), I get Division by Zero error I think you've misdiagnosed the problem. The error will occur when and only when `$rec{'Innings'} == $rec{'NotOut'}` - ie for cricketers who have never been dismissed, irrespective of how many runs they've made. Cheers, Rob	[reply] [d/l]
Re: Null values in Perl Calculation by hippo (Archbishop) on May 03, 2024 at 07:49 UTC
Welcome to the Monastery, PaulB-Liverpool. In addition to the good replies you have already received, I will suggest that `$baverage1` is not a great name for that variable. It seems to contain the number of dismissals and not an average of any kind whatsoever. Perhaps `$dismissals` or even the concise `$outs` would be better. And, in case you were unaware, you do not need all those single quotes inside the hash keys. 🦛	[reply] [d/l] [select]
Re: Null values in Perl Calculation by BillKSmith (Monsignor) on May 03, 2024 at 15:20 UTC
Syphilis has identified a special case where this average does not exist. tybalt89 proposed a solution which avoids the error by bypassing the calculation. With this correction, your existing code would output a numeric zero. This may be a problem for your users because they could not tell the difference between an average of zero and no average. I recommend that you ask them what they would prefer. Other possible choices include: Omit record Output a null string Ouput a string of blanks Output a special string ('***' or '-----') Except for the first, you could use `$baverage = $baverage1 ? $rec{'BatterRuns'} / $baverage1 : '***';` [download] Bill	[reply] [d/l]
Re: Null values in Perl Calculation by PaulB-Liverpool (Initiate) on May 04, 2024 at 01:16 UTC
Thanks all; particularly tybalt89 who solved my logic problem! And yes, variables have been renamed as suggested. I'm a starter; big style! I managed to sort out making the average readable to 2 decimals om my own (it took a while). I like it here... it's like the internet used to be! Thanks.	[reply]