t; |3|9 12 |
> +-+-+
> |0|11 15|
> +-+-+
> |5|14 16|
> +-+-+
>
>
> R.E. Boss
>
>
> -Original Message-
> From: Programming On Behalf Of
> Raul Miller
> Sent: donderdag 27 januari 2022 19:1
:11
To: Programming forum
Subject: Re: [Jprogramming] Find nth duplicate in vector
Well, ... the implementation posted by xash is very nice, but in
http://jsoftware.com/pipermail/programming/2022-January/059790.html
Pawel Jakubas specified that the value appears first, and the index appears
second
Well, ... the implementation posted by xash is very nice, but in
http://jsoftware.com/pipermail/programming/2022-January/059790.html
Pawel Jakubas specified that the value appears first, and the index
appears second, and that the indices start with 1 for the first value.
Also, somewhere along the
I wonder why there’s still so much traffic on this thread
(okay, I’m to blame for quite some of it)
I thought xash published the best correct solution.
Am I wrong?
Am 27.01.22 um 18:42 schrieb 'Mike Day' via Programming:
Pawel Jakubas has moved on to something else in his correspondence,
Pawel Jakubas has moved on to something else in his correspondence, presumably
related to
this topic.
Anyway, I think we need his adjudication, as I don't think Raul Miller's f is
doing what PJ asked
for.
Hauke Rehr's proposal is
hrf =: {{ (,~ {) {. I. (>: x) e."1 +/\ =/~ y }}
My latest
Here's how I would modify my implementation to produce an empty result
when a non-duplicate is referenced.
d=: 1 _1 2 3 4 2 5 6 3 8 10 3 2
f=: {{y ({~,]) I. wrote:
>
> Perhaps I should point out that my verb, h (see below), uses a lot of space
> for a large list, especially if there are
Perhaps I should point out that my verb, h (see below), uses a lot of space
for a large list, especially if there are few repeats, as it’s using an outer
product.
I later produced an even more verbose effort which runs in less space on a 10^6
long vector, but takes 3-4x the space & time
Unfortunately, Pawel wants 2 f d to be 3 11. However, I find that 3 f d IS 3
11.
Other results are a bit strange, too:
4 f d
2 12
8 f d
|index error: f
| y({~,])x i.~+/\(i.@#~:i.~)y
I wasn’t going to post my effort, but it might interest Pawel. This version
works on the
-.@~: gets a mask of duplicates, I. then their indices.
With them you can get a list of (index, value) pairs:
((],.{~) I.@:-.@~:) a
5 2
8 3
11 3
12 2
With 0 ({ (],.{~) I.@:-.@~:)) a you can 0-index into this list.
If you are only interested into the first duplicate of a value,
you could filter
As Henry pointed out,
do take a look at [1] for how to approach this in J
If you want to understand my solution,
just try it step by step.
I repeat it here, with a bit of litter removed:
f =: {{ (,~ {) {. I. (>: x) e."1 +/\ =/~ y }}
NB. where does each number occur?
=/~ d
1 0 0 0 0 0 0 0
Here's a variation that works:
d=: 1 _1 2 3 4 2 5 6 3 8 10 3 2
f=: {{y ({~,]) x i.~ +/\(i.@#~:i.~)y }}
1 f d
2 5
2 f d
3 8
The phrase (i.@# ~: i.~) finds the locations of duplicates
(i.@#~:i.~) 1 _1 2 3 4 2 5 6 3 8 10 3 2
0 0 0 0 0 1 0 0 1 0 0 1 1
And, +/\ computes a running sum
It should be of course
1 f d
2 5
Would be great if you could decompose your solution and the idea behind the
solution. Many thanks.
Cheers,
Pawel
--
For information about J forums see http://www.jsoftware.com/forums.htm
Use the ideas in
https://code.jsoftware.com/wiki/Essays/Progressive_Index-Of .
Henry Rich
On 1/26/2022 1:37 PM, Pawel Jakubas wrote:
Dear J enthusiasts,
I wonder how to elegantly implement dyad f that takes as x=1,2,3... and y
vector and returns nth duplicate value with index of that
Maybe this is what you want (but it’s not elegant)
f =: {{ (,~ {) {. I. ( (>: x)"1) +/\ =/~ y }}
1 f d
2 5
2 f d
3 11
just a quick and dirty working solution
(if 2 5 is the correct answer to 1 f d)
Am 26.01.22 um 19:37 schrieb Pawel Jakubas:
Dear J enthusiasts,
I wonder how to
I don’t understand why it’s index 2 (first occurrence of 2)
but 11 (third occurrence of 3)
Am 26.01.22 um 19:37 schrieb Pawel Jakubas:
Dear J enthusiasts,
I wonder how to elegantly implement dyad f that takes as x=1,2,3... and y
vector and returns nth duplicate value with index of that
Dear J enthusiasts,
I wonder how to elegantly implement dyad f that takes as x=1,2,3... and y
vector and returns nth duplicate value with index of that occurence:
d=: 1 _1 2 3 4 2 5 6 3 8 10 3 2
NB. the earliest first duplicate is for 2 and index 2
1 f d
2 2
NB. the earliest second
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