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Asked: 2026-05-15T21:25:04+00:00

Question abstract: how to parse text file into two hashes in Perl. One store

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Question abstract:

how to parse text file into two “hashes” in Perl. One store key-value pairs taken from the (X=Y) part, another from the (X:Y) part?

1=9  
2=2  
3=1  
4=6  
2:1  
3:1  
4:1  
1:2
1:3  
1:4  
3:4  
3:2

they are kept in one file, and only the symbol between the two digits denotes the difference.

===============================================================================

I just spent around 30 hours learning Perl during last semester and managed to finish my Perl assignment in an “head first, ad-hoc, ugly” way.

Just received my result for this section as 7/10, to be frank, I am not happy with this, particularly because it recalls my poor memory of trying to use Regular Expression to deal with formatted data, which rule is like this :

1= (the last digit in your student ID,or one if this digit is zero)  
2= (the second last digit in your student ID,or one if this digit is zero)
3= (the third last digit in your student ID, or one if this digit is zero)
4= (the forth last digit in your student ID, or one if this digit is zero)

2:1 
3:1  
4:1  
1:2  
1:3  
1:4  
2:3 (if the last digit in your student ID is between 0 and 4) OR
    3:4 (if the last digit in your student ID is between 5 and 9)
3:2 (if the second last digit in your student ID is between 0 and 4) OR
    4:3 (if the second last digit in your student ID is between 5 and 9)

An example of the above configuration file: if your student ID is 10926029, it has to be:

1=9  
2=2  
3=1  
4=6  
2:1  
3:1  
4:1  
1:2
1:3  
1:4  
3:4  
3:2

The assignment was about Pagerank calculation, which algorithm is simplified so I came up with the answer to that part in 5 minutes. However, it was the text parsing part that took me heaps of time.

The first part of the text (Page=Pagerank) denotes the pages and their corresponding pageranks.

The second part (FromNode:ToNode) denotes the direction of a link between two pages.

For a better understanding, please go to my website and check the requirement file and my Perl script here

There are massive comments in the script so I reckon it is not hard at all to see how stupid I was in my solution 🙁

If you are still on this page, let me justify why I ask this question here in SO:

I got nothing else but “Result 7/10” with no comment from uni.

I am not studying for uni, I am learning for myself.

So, I hope the Perl gurus can at least guide me the right direction toward solving this problem. My stupid solution was sort of “generic” and probable would work in Java, C#, etc. I am sure that is not even close to the nature of Perl.

And, if possible, please let me know the level of solution, like I need to go through “Learning Perl ==> Programming Perl ==> Master Perl” to get there 🙂

Thanks for any hint and suggestion in advance.

Edit 1:

I have another question posted but closed here, which describes pretty much like how things go in my uni 🙁

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1 Answer

  1. Editorial Team

    Is this what you mean? The regex basically has three capture groups (denoted by the ()s). It should capture one digit, followed by either = or : (that’s the capture group wrapping the character class [], which matches any character within it), followed by another single digit.

    my ( %assign, %colon );

while (<DATA>) {
    chomp;                     
    my ($l, $c, $r) = $_ =~ m/(\d)([=:])(\d)/;

    if    ( q{=} eq $c ) { $assign{$l} = $r; }
    elsif ( q{:} eq $c ) { $colon{$l}  = $r; }
}        

__DATA__
1=9  
2=2  
3=1  
4=6  
2:1  
3:1  
4:1  
1:2
1:3  
1:4  
3:4  
3:2

    As for the recommendation, grab a copy of Mastering Regular Expressions if you can. It’s very…thorough.

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