On 28.02.2022 23:51, Axel Reichert wrote:
> Kaz Kylheku <480-992-1380@kylheku.com> writes:
>
>> 1> (flow (range 1000 9999)
>> (keep-if [chain digits (ap > (+ @2 @3) (+ @1 @4))])
>> (partition-if (op neq 1 (- @2 @1)))
>> (find-max @1 : len))
>
> Interesting, how close a Lisp can get to my original pipeline. Thanks!

I'm unfamiliar with this syntax, but this looks a lot like the general
approach to tackle the task, the one that I had (informally) described
with

seq 1000 9999 | awk '
{ gsub(/./,"& ") }
{ r=r ($1+$4 < $2+$3) }
{ split(r,a,/0+/) }
END { ...sorting of or maximum in array a... }
'

and not so much like this band-worm (your "original pipeline")

seq 1000 9999 \
| sed 's/\(.\)/\1 /g' \
| awk '{if ($1+$4 < $2+$3) {print 1} else {print 0}}' \
| tr -d '\n' \
| tr -s 0 '\n' \
| sort \
| tail -n 1 \
| tr -d '\n' \
| wc -c

which is full of primitive text processing tools (tail, many tr) that
have no counterpart in the high-level-language lisp code.

Opinions obviously differ.

Janis

>
> Axel
>

On 23.02.2022 22:44, Axel Reichert wrote:
> Janis Papanagnou <janis_papanagnou@hotmail.com> writes:
>> On 20.02.2022 20:35, Axel Reichert wrote:
>
>> I'd nonetheless had used 'sort -r' and 'head -n 1'
>
> Understood, great: "sort" does not care about the "-r", because it just
> negates the "predicate", but printing the first line is both cheaper and
> easier for awk. It seems you have learned a thing or two about Big Oh
> notation. (-;

Since you mention "Big Oh"; note that sorting (O(N log N) or O(N^2))
is more expensive than a linear find (O(N)). In case of your sample
application that you proposed in this sub-thread it may be practically
irrelevant (nowadays) to consider that, since we process only 9000
data lines. But if I want to handle larger data sets that's another
reason to prefer a simple maximum determination instead of sorting.
Just BTW. (Yes, "Big Oh" is crucial. I've heared that in interviews
for Google jobs it's also a central and important element.)

>
> I tend to neglect this, being used to much larger number crunching
> efforts than the modest 10^4 numbers here. Thanks for reminding me.
>
>> build binary string r=r ($1+$4 < $2+$3)
>
> Great, another feature that I tend to forget, the default string
> concatenation. Very elegant in combination with the C-style boolean.
>
>> seq 1000 9999 | awk '
>> { gsub(/./,"& ") }
>> m=($1+$4 < $2+$3) { if (++c>max) max=c }
>> !m { c=0 }
>> END { print max }
>
> Great. That kind of stuff I was after and eager to learn!
>
>> (Ah, okay, you want the numbers also generated by awk. I assumed that
>> 'seq' was just an example input source that could be in principle any
>> process or file as data source.
>
> In general I agree, but here it is one of the conceptual obstacles in my
> way of thinking. So far I believe there did not come up any post in this
> thread that shows how to "feed" output from the BEGIN block to the rest
> of the "awk" program. Or did I miss something?

I'm not sure I understand what you wrote here. If you are saying that
you want to generate the sequence numbers in the BEGIN block and pass
them to the implicit awk-processing-loop then yes, that's not possible.
You would then do the whole processing in the BEGIN block using a loop;
I think I've seen someone in this sub-thread posting such a loop-based
awk-solution.

Personally I tend to and intuitively separate data generation from the
data processing as consequence of a design and usability experience;
that's why it didn't occur to me (before I saw your post) that it was
part of the "code puzzle".

Janis

On 23.02.2022 22:44, Axel Reichert wrote:
> Janis Papanagnou <janis_papanagnou@hotmail.com> writes:
>
>> build binary string r=r ($1+$4 < $2+$3)

(I forgot to comment on that. - A caveat for the general case here.)

> Great, another feature that I tend to forget, the default string
> concatenation. Very elegant in combination with the C-style boolean.

Since we were talking about "Big Oh"... - Note that in case of large
strings or data sets such concatenations can be expensive (depending
on the Awk version you use). GNU Awk has a built-in optimization for
the x = x ... cases of concatenations, though, so it's cheap here.

Janis

Janis Papanagnou <janis_papanagnou@hotmail.com> writes:

> If you are saying that you want to generate the sequence numbers in
> the BEGIN block and pass them to the implicit awk-processing-loop

Yes.

> then yes, that's not possible.

O. K., thanks.

> You would then do the whole processing in the BEGIN block using a loop;
> I think I've seen someone in this sub-thread posting such a loop-based
> awk-solution.

Yes, you maybe right.

> Personally I tend to and intuitively separate data generation from the
> data processing as consequence of a design and usability experience

Makes sense.

Best regards

Axel