Note also that the usual lookup pattern is
(reference i. values) { lookup
For example:
(2 3 5 7 i. 2 3) { 'this';'is';'a';'test';'...'
But, there are many variations on this theme.
--
Raul
On Mon, Feb 18, 2013 at 12:20 AM, Devon McCormick <[email protected]> wrote:
> At the risk of repeating much of what Raul said, here are some short
> versions of answers to your questions:
>
> 1. Using a list like
> 1 2 3 4
> a pointer to the last element could be "_1{" .
>
> 2. see 1 above and Raul's reply - it's not clear why these elements need to
> be nested.
>
> 3. You could build some kind of hashmap if you needed it but, as with
> linked-lists, this is usually a means to an end, not an end in itself. If
> you have an example of what you're trying to accomplish with a hashmap (or
> a linked list), there's either a simpler way to accomplish it in J or an
> interesting problem for the forum to ponder.
>
>
> On Sat, Feb 16, 2013 at 4:42 PM, Raul Miller <[email protected]> wrote:
>
>> It's worth talking about, I think, the distinction between a "linked
>> list" and a "list".
>>
>> First, why would you prefer a linked list over a list? Efficiency?
>> If so, note that regular lists can have performance an order of
>> magnitude better than linked lists in many contexts. The efficiency
>> of linked lists comes into play when your algorithms are designed to
>> be efficient for a linked list and inefficient for a flat list.
>>
>> Hashes are similar, but even more complex (as a general rule, hashes
>> have extremely bad worst case behavior, and there have been a variety
>> of denial of service attacks for web servers because of this issue -
>> nowadays, a robust web server randomizes its hashing algorithm to make
>> it hard to guess how to break it).
>>
>> In other words, both of these are typically examples of complex
>> solutions - it's probably a mistake to start here, and probably wiser
>> to start with specific applications. (Though, if your applications
>> are simply designed to require these kinds of data structures, it's
>> not clear why you would be using J to implement them.)
>>
>> Or... that's my current understanding of these issues.
>>
>> FYI,
>>
>> --
>> Raul
>>
>> On Sat, Feb 16, 2013 at 12:57 PM, Y-01 <[email protected]> wrote:
>> > hi@all
>> >
>> > I have some basic questions on which i can't find any answers
>> >
>> > 1. How we can create a linked list with push_back complexity =~ O(1) in
>> J ?
>> > we need to save a poinet to last element
>> >
>> > 2. is it right that these examples correspond to linked lists?
>> >
>> > 1;<2
>> > 1;<(2;<3)
>> > 1;<(2;<(3;<4))
>> >
>> > 3. And what about hashmap? Is it right that there is no any builtined
>> > hashmap struct? Maybe there is a popular aside addon/lib (smth like
>> > hash.ijs) ?
>> > ----------------------------------------------------------------------
>> > For information about J forums see http://www.jsoftware.com/forums.htm
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
>>
>
>
>
> --
> Devon McCormick, CFA
> ^me^ at acm.
> org is my
> preferred e-mail
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
----------------------------------------------------------------------
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