Question

Merge / insert into hashtable

Asked by: Daij-Djan

How can I modify an already built hashtable I get back from a function effeciently!?

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Asked On
2004-05-06 at 05:40:43ID20980098
Tags

hashtable

,

merge

,

insert

Topic

Java Programming Language

Participating Experts
5
Points
125
Comments
15

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Answers

 

by: indigostarkPosted on 2004-05-06 at 05:47:31ID: 11005051

Could you post some code?

 

by: WebstormPosted on 2004-05-06 at 05:56:54ID: 11005120

 

by: zzynxPosted on 2004-05-06 at 06:19:32ID: 11005268

>> How can I modify an already built hashtable I get back from a function effeciently!?
Use all the functions a hashtable has

 

by: Daij-DjanPosted on 2004-05-06 at 06:28:07ID: 11005339

class b
{
 Hashtable foo() { ... }
}

class C
{
 Hashtable foo() { ... }
}

class A
{
 void bar()
 {
   Hashtable b = B.foo();
   Hashtable c = C.foo();
 
   //merge b and c - insert c at the top of b
   //any way to do that other than using put or 'putall'
}

 

by: zzynxPosted on 2004-05-06 at 06:30:07ID: 11005350

>> //any way to do that other than using put or 'putall'
you mean no add() and addAll()?
Why is that?

 

by: zzynxPosted on 2004-05-06 at 06:41:20ID: 11005438

No, you mean put() and putAll().
Well, I think that are the only functions to add elements.
Why don't you want to use them?

 

by: Daij-DjanPosted on 2004-05-06 at 06:56:22ID: 11005563

The hashtables are large and joining to hashtables using put would be very inefficient even for java standards - I wanted to use a more 'lowlevel' approach.

There is for arrays

 

by: zzynxPosted on 2004-05-06 at 07:07:06ID: 11005665

>> There is for arrays
You mean?

Are you looking for some conversion to array, join them and convert to hashmap again?
Don't understand. sorry

 

by: mayankeaglePosted on 2004-05-06 at 07:09:16ID: 11005690

The best approach I see is nothing but putAll (). Because even if you want to obtain an array out of the hash-table and then merge the values and then again add them to a hash-table, remember that you will have to do that for keys and values as well - and you will need to keep track of each key/ value pair. Moreover, putting it back into a new hash-table would ensure that this process turns out to be more expensive that a simple call to putAll () ;-)

 

by: maheshexpPosted on 2004-05-06 at 07:11:51ID: 11005716

i didn't feel anything lazy using hashtables...what made u to feel so

just a suggestion. the recent java 1.5 has many features for sets and list has many features such as

# Special-purpose Map and Set implementations are provided for use with typesafe enums.
# Special-purpose copy-on-write List and Set implementations have been added.
# Wrapper implementations are provided to add dynamic type-safety for most collection interfaces.
# Several new algorithms are provided for manipulating collections.
# Methods are provided to compute hash codes and string representations for arrays.

so writing ur own available things from scratch is waste of time, and in future, it will be still imporved and u will see improvements.

 

by: Daij-DjanPosted on 2004-05-06 at 07:17:37ID: 11005786

ok - so ..... put it will be......

 

by: zzynxPosted on 2004-05-06 at 07:25:18ID: 11005871

So you mean:

void bar()
 {
   Hashtable b = B.foo();
   Hashtable c = C.foo();
 
   HashTable t = new HashTable();
   t.putAll(c);
   t.putAll(b);
}

 

by: zzynxPosted on 2004-05-06 at 07:26:38ID: 11005886

Maybe better:

    HashTable t = new HashTable( c.size() + b.size() );

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