korak has asked for the wisdom of the Perl Monks concerning the following question:

Multiarray does not read correct value from a table. The problem is the following. I am trying to use the value read from a csv table into a formula to calculate latitude. The problem is that when I f.ex print the multiarray like this: print $multiarray[2][15] it shows the correct value. But if I am using the while function to step i for each line it will only print the value for $multiarray[0][15] even if I have set it up to print like this: $multiarray[i][15]. I have even set up a print to get the value of i like this print $i. And i has the correct number. What can be the problem here? 

                    $multiarray[i][15] =~ s/\,/./g;
                    print "array is $multiarray[2][15] and multiarray 
+15 is $multiarray[i][15] and then the number i is $i\n";
                    $latitude = ((($multiarray[i][15]) / 90) * 8388608
+);
                                print "i is $i and latitude $latitude 
+and latitude $latitude2 and longitude $longitude\n";
                    $latitude2 = ceil($latitude);
                                print "i is $i and latitude $latitude 
+and latitude $latitude2 and longitude $longitude\n";

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The problem is not that "i" doesnt have the correct value...it does. But multiarray seems to be stuck on the first value read into the variable. I am also exchanging a comma with a dot on the variable to be able to read it and calculate correctly. That seems to be fine too. Any suggestions?

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Re: Multiarray does not read correct value from a table
by 2teez (Vicar) on Jun 20, 2013 at 07:24 UTC

    Hi korak,
    With the amount of infomation given, it is hard to tell, where the issue is, since you are not showing, your multi-array data and how you are "stepping" through them.
    However, I can only suspect, that your variable $i is NOT increasing.
    Moreover, are you not suppose to use variable $i instead of i. Please, check your code in the following line: 

       $multiarray[i][15] =~ s/\,/./g;  ## HERE
   $latitude = ((($multiarray[i][15]) / 90) * 8388608); ## And HERE

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    Please, it is better practice to also use warnings and strict in your Perl script.

    If you tell me, I'll forget.
    If you show me, I'll remember.
    if you involve me, I'll understand.
    --- Author unknown to me
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Re: Multiarray does not read correct value from a table
by kcott (Archbishop) on Jun 20, 2013 at 07:16 UTC

    G'day korak,

    You haven't really shown enough code; however, i is wrong — you probably want $i.

    -- Ken

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      I am a bit embarrassed to say: i was the problem. I forgot to use the variable $i in the multiarray. No wonder it didn't step up. Thanks a lot guys!

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Re: Multiarray does not read correct value from a table
by hdb (Monsignor) on Jun 20, 2013 at 07:22 UTC

    These kind of problems are easy to spot if you use strict; and use warnings;.

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Re: Multiarray does not read correct value from a table
by AnomalousMonk (Archbishop) on Jun 20, 2013 at 11:51 UTC

    Others have already advised you to use the strict and warnings pragmata. Do yourself a big favor and heed this sage advice. (If you're a beginning Perler, the diagnostics module is a good adjunct to warnings.) Here's why: 

    >perl -le
"my @mra = ( [ qw(a b eye c) ],  [ qw{w x y z} ], );
 ;;
 print qq{'$mra[1][2]'};
 print qq{'$mra[i][2]'};
"
'y'
'eye'

>perl -le
"use warnings;
 ;;
 my @mra = ( [ qw(a b eye c) ],  [ qw{w x y z} ], );
 ;;
 print qq{'$mra[1][2]'};
 print qq{'$mra[i][2]'};
"
Unquoted string "i" may clash with future reserved word at -e line 1.
'y'
Argument "i" isn't numeric in array element at -e line 1.
'eye'

>perl -le
"use warnings;
 use strict;
 ;;
 my @mra = ( [ qw(a b eye c) ],  [ qw{w x y z} ], );
 ;;
 print qq{'$mra[1][2]'};
 print qq{'$mra[i][2]'};
"
Bareword "i" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.

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    In the presence of strictures, this particular mistake does not even compile. This, IMHO, is the best possible fate for this code. It's nice to have a warning, but a warning is only generated if the code is executed, and the particular code producing a warning may only be traversed on a daily/weekly/monthly basis. You may find yourself plowing through an enormous log file in search of some clue to a transient problem. Some even take the extra step of escalating all warnings to fatality, so at least a warning will be the last entry in a log file concerning a particular program. Caveat programmor.

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