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Hash Reverse

kaalraa

Hello,

Does anyone know as how to get the reversal of hash in Perl. I only want the reversal to be done on keys not the value as value can be an array as well.

The situation is that we have a function in which it reads out a certain DCR, which has the structure somewhat like the undergiven. Large container is Questions which has an element Question and a container Paragraphs having element as Para. Logic behind that a single query can has multiple para answers to it.

QUESTIONS >> [QUESTION]
[PARAGRAPH >> PARA]

I am reading the DCR and making Question as key and paragraph as value array with multiple para as a hash. I pass this on to the perl script which has to read the hash and display the content. Problem we are facing is when i try to read the hash it starts from the last question extered as a key in the hash. I just want to revert the hash with reference only to its key.

Any help or suggestions are welcome.

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Comments

jbonifaci

How are you storing the "multiple paragraphs"? If it's in a hash, what are you using for the key/value?

I would recommend not using a hash if the order means anything, as hashes do not preserve order, unless you name your keys paragraph1, paragraph2, etc. But that would really defeat the purpose of using a hash and would lean towards using an array. That being said, you should likley be using an array to store your paragraphs.

So to answer your question, there is no "reverse" for hashes, as hashes have no sense of order.

~Jeff

kaalraa

As key it is the QUESTION and as VALUE is an array of answers. Can you suggest me any other way of its implementation.

jbonifaci

So what is your problem exactly. Is your array of answers in the wrong order? If so, why not look where you are building the array and build it in the correct order. If you don't want to do that, just use "reverse" on the array.

~Jeff

kaalraa

Jeff,

The problem i am facing is not about the order of answers in array, but its about the questions as the keys of hash.

For example, data when put in DCr is in the following order:
First Question
>> First Answer Para
Second Question
>> Second First Para
>> Second second Para

But when I retrieve the hash, it gives me "Second Question" before "First Question" in order, whereas the answers are always associated with correct question and in correct order as well. ITS only the hash keys (which are QUESTIONS) that does not come in the order on which its put in.

jbonifaci

Ok, so that goes back to the point I made before, hashes are not arrays and arrays are not hashes. If you want to preserve the order, you should be using an array.

So create an array called something like @QuestionArray. Then for each question, create a temp hash with 2 keys 'question' and 'answers'. The value of 'question' will be the question and the value of 'answers' will be an array of answers. Then push this temp hash into your array. This will preserve the order.

~Jeff

kaalraa

Thanks Buddy!!

Ok, so that goes back to the point I made before, hashes are not arrays and arrays are not hashes. If you want to preserve the order, you should be using an array.

So create an array called something like @QuestionArray. Then for each question, create a temp hash with 2 keys 'question' and 'answers'. The value of 'question' will be the question and the value of 'answers' will be an array of answers. Then push this temp hash into your array. This will preserve the order.

~Jeff

Adam Stoller

Jeff,

The problem i am facing is not about the order of answers in array, but its about the questions as the keys of hash.

For example, data when put in DCr is in the following order:
First Question
>> First Answer Para
Second Question
>> Second First Para
>> Second second Para

But when I retrieve the hash, it gives me "Second Question" before "First Question" in order, whereas the answers are always associated with correct question and in correct order as well. ITS only the hash keys (which are QUESTIONS) that does not come in the order on which its put in.

So you have a hash of hashes - when you really want a hash of arrays (insert "references to" anywhere within the preceeding statement) - hashes, are by their very nature, un-ordered. So you want something like:

my %QandA = (
    "First Question" => ["First Answer Para"],
    "Second Question" => ["Second First Para",
                          "Second Second Para"],
    ...);

jbonifaci

Actually Adam, if you follow the posts all the way down, that's actually what he had already. The problem was with the order of his questions, not his answers. What he really wanted was:

my @QuestionArray = (
{
  'question' => 'Q1',
  'answers' => ['Q1 A1', 'Q1 A2', 'Q1 A3']
},
{
  'question' => 'Q2',
  'answers' => ['Q2 A1', 'Q2 A2', 'Q2 A3']
},
{
  'question' => 'Q3',
  'answers' => ['Q3 A1', 'Q3 A2', 'Q3 A3']
},
...
);

Just wanted to clear up any confusion.

~Jeff

Adam Stoller

Actually Adam, if you follow the posts all the way down, that's actually what he had already. The problem was with the order of his questions, not his answers. What he really wanted was:
...
Just wanted to clear up any confusion.

~Jeff

Heh - timing problem - I started responding after 10:10 post, but got interrupted and didn't finish until after the other posts had made it out there (which I hadn't seen until just now).

So it wasn't just a hash-of-arrays, it was an array-of-hashes-with-arrays. The outer-most level to order the questions, and the inner-most level to order the answers for each question.