AltME groups: search

it is normal that hash! will only hash "keys" of assoc on first level, 
if you want on sublevels you can iterate the list and turn it into 
hashes acordingly .. if you have a lot of data hash is a lot faster 
650x in this test http://www.rebol.com/article/0020.html

Sometimes I return a hash index as a query result set, for database-like 
functions. If I had to use an assoc instead I'm sure it would be 
fine as long as select was still O(1) like a hash.

Most of the time I use it like an assoc, or like a fully indexed 
table.

The main advantage a hash has over an assoc is that you aren't limited 
to simple key-value records, you can use longer records.

I would want an assoc to be able to have any string type as a key 
and words as well, at least.

The main advantage a hash has over an assoc is that you aren't limited 
to simple key-value records, you can use longer records.
 - yes, that is the domain where hash! should be better

Still, if assocs are drastically faster it would be worth it. I could 
use blocks or lists and assoc indexes if I need them.

Assoc indexes to lists would be useful, as useful as I've found hash 
indexes to lists to be. I'd use hashes and lists more often if block 
parsing worked on them.

Jamie, that was referring to using a hash as a table rather than 
as an index. If you use a hash rather than a block for your table, 
all of your searches would be faster without needing any seperate 
indexes. The only way to have the speed of searching a block be comparable 
would be to keep it sorted and use a binary search (what RebDB does 
I think), but that doesn't help much with multiple keys that require 
different sorting orders.


On the other hand, I've been sold on the idea that when you use a 
hash as an index (rather than the table), you are basically using 
it like an assoc, so using a structure optimized for that behavior 
would probably be best.

As for the hash (or assoc) index and list data combo, it has some 
advantages. When you are inserting and removing data a lot lists 
have a known speed benefit but the real advantage as far as indexes 
are concerned is in how lists handle series offsets (I'm using the 
word offset here because I'm using the word index to refer to the 
external hash/assoc index).


Blocks encode their offsets as a number offset from the beginning 
of the series:

>> a: [a b c]
== [a b c]
>> b: skip a 2
== [c]
>> index? b
== 3
>> insert next a 'd
== [b c]
>> b
== [b c]
>> index? b
== 3

List offsets are pointers to the associated list element.

>> a: make list! [a b c]
== make list! [a b c]
>> b: skip a 2
== make list! [c]
>> index? b
== 3
>> insert next a 'd
== make list! [b c]
>> b
== make list! [c]
>> index? b
== 4


If you are indexing your data and your data in in a block, you need 
to update your index with almost every insertion and removal because 
the references to latter positions of the block in the index will 
be invalid. With list insertion and removal, external references 
are likely to still be valid unless the referenced elements themselves 
are deleted. If you are sure to delete the reference from the index 
(or replace it with nones) the rest of the index should be OK. New 
index references can just be tacked on the end, or put into the first 
empty entry. This makes live indexes a lot more practical.


On the down side, if you are using lists and they are long enough 
to make linear searches impractical, you really do need an external 
index for them to be useful. Also you need to balance the overhead 
and complexity of keeping the indexes updated against their benefit. 
This technique is not for the faint of heart unless you can get some 
guru to do algorithms for you.

>> do %mezz/filter-html.r
Script: "HTML Filter" (none)
** Script Error: macro has no value

** Near: !set-assoc: macro [assoc word value] [(:either) _pos: (:find) 
assoc word [(:poke) _pos 2 value/only] [
        insert/on..