World: r3wp

sorry if I will propose a nonsense, or if the solution already exists, 
but - when using REBOL for data extraction (using parse) and forming 
a block or CSV as a result, I often come to the need of append-only-if-the-item-does-not-exist-already, 
so using following idiom:

if not found? find target value [append target value]


What about adding /not refinement (or other name), so that I could 
append only unique values?

Also - is there any way of how to easily find out, if the block is 
unique? Should I apply 'unique, and compare the length before and 
after? Pity 'unique has /skip refinement, but does not have /compare 
one (as 'sort has), so that I can't set, when I have e.g. record 
of 5 items, I want to 1) set the record size (/skip) 2) select fields, 
upon which we want to define uniquess - could be an integer offset, 
or a block of positions [1 3] ... 'sort allows at least the offset 
via /compare

Two partial workarounds to your first issue Petr (I've used them 
both or various data sets):


1.  simply APPEND each time, then when the set is complete use UNIQUE 
to deduplicate

2.  if not alter target value [append target value]
   this ensures that VALUE is the last entry in TARGET

2 is more efficient, since UNIQUE always copies.

but as for efficiency, does the alter really differs from "if not 
found? find?"

ALTER removes a value, if it's found.

which is the reverse, but the same, as appending only in the case, 
if not found :-)

ALTER is not really useful in its current form.

I found not use ALTER as it's not native.. I usually use the solution 
UNIQUE where the block is not much large, but if efficiency is needed, 
I would just go with:

unless find blk val [append blk val]

(I found = I would)

I don't want to add new refinements for such a easy to do solutions 
as they would slow every APPEND a little bit.

it is just, at least for me, when using append at all - it is very 
often used idiom ...

some people prefer this construct

all [
	find blk val
	append blk val
]

that would be ANY instead of ALL.

oh yeah :)

two characters shorter than Oldes' solution

that's programmer's solution, but it does not read as nicely as - 
if not found? find blk val [append blk val] :-)

yes, Oldes' version reads even nicely ...

Who says?

These are just idioms ...

I always have to think twice or more when i come across 'unless :)

And I have to think more than twice, when using combination of NOT 
ALL, NOT ANY :-)

Can I somehow get a difference of two blocks, with different sizes? 
Trying to avoid loops, but I will use loop most probably anyway ...

blk1 structure: [contract user tarif]
blk2 structure: [contract user street town tarif]


I know there are functions like intersect/difference, they even have 
/skip refinement, but those most probably can't treat different record 
sizes?

Graham, you are not english native speaker? For me it's easy.. I 
learned that UNLESS = IF NOT and so I use it:) http://www.edufind.com/english/grammar/IF9.cfm

I remember UNLESS from extended basic of ZX Spectrum. And I lowed 
the word itself, dunno why :-)

Are you looking for this?

>> difference [contract user tarif] [contract user street town tarif]
== [street town]

or what result do you expect?

no, sorry ... those are just structures, but blocks contain real 
data, hundreds and thousands of records ...

but never mind, I will use loop and look-up, no problem, just laziness 
:-)

unless is one more character than if not .. so why use it?

I guess, that what Pekr wants should be implemented carefully, otherwise 
it may end up being slow...

Graham.. that's easy... because UNLESS is faster then IF NOT

I really think, again, that  'append-or-insert-only-if-the-item-does-not-exist-already 
 should be a native in R3.


its a function MOST of us would use on a frequent basis.  it would 
be very usefull and its very powerfull with a /skip refinement

agreed ...

As opposed to that, my opinion is, that it should not be a native, 
since no significant speedup against a mezzanine would be observable

we can start with a mezz... but because of the find and then insert/tail 
and all the possible refinements its needs to handle... overall, 
it will be faster as a native.

this function will often be used in loops, and the less functions 
and REBOL stack usage you have the bigger the speed gains.

Yes, I agree that it would be useful built in. (Whether it's native 
or mezz, doesn't really bother me.)

(Graham, "unless" = 6 chars = "if not")

ascii printable characters ... we are talking about saving ink here!

yes and LCD fatique too

No body wants "unless" burnt into their screens!

I would like to see a version of REBOL where only the bare minimum 
natives are implemented and everything else is a mezz. It's possible 
that REBOL would run many months faster if not preamturely optimized. 
;-)

I'd be interested in seeing how small an executable could be made, 
if utterly everything was stripped, even file and network access.

That might be interesting, but not terribly useful.

well, then you can say that you can fit your software on a floppy 
and wave a 5.25" floppy in people's faces :-)

We can do that now. Base is ~270K.

It's really hard, now, to find media small enough to make an "it 
fits" claim. :-) I think the smallest memory sticks I have are 64MB.

I wonder if you can fit a script onto those square barcodes.

sure....