Wow! The black hole of J strikes again...
On Mon, 22 Sep 2008, Roger Hui wrote:
gg2a=: 4 : 0
b=. |:x I.&> }:y
(b +//. {:y) (<"1 ~.b)} (>:#&>x)$0
)
x=: /:~&.> 5 7 13 [EMAIL PROTECTED]&.> 1000
y=: 4 1000 [EMAIL PROTECTED] 1000
x (gg2a -: Gg2) y
1
See http://www.jsoftware.com/jwiki/Essays/Key
for some uses of "key".
----- Original Message -----
From: "J. Patrick Harrington" <[EMAIL PROTECTED]>
Date: Monday, September 22, 2008 19:44
Subject: Re: [Jgeneral] A Sorting Problem
To: General forum <[email protected]>
Thanks, Raul! I've replaced the old Gg with Gg2:
Gg2=: 4 : 0
'f1 f2 f3'=. x
'a1 a2 a3 a'=. y
b=. (f1 I. a1),.(f2 I. a2),.(f3 I. a3)
sums=. b +//. a
idx=. <"1 ~. b
'n1 n2 n3'=. >: >#&.> f1;f2;f3
sums idx} S=. (n1,n2,n3)$0
)
and now the sort adds negligible time to the program.
I need to learn about "key".
Patrick
On Mon, 22 Sep 2008, Raul Miller wrote:
On Mon, Sep 22, 2008 at 3:14 PM, J. Patrick Harrington
<[EMAIL PROTECTED]> wrote:
So the problem looks like this: a -- intensity array,
size = np (nphotons >
1e5)
a0, a1, a2 -- tags for position & angle, all size np
f0, f1, f2 -- boundaries of the cells into which I want
to sort the the photons.
Thus, b0=. f0 I. a0 will be the index which shows into
which f0 interval
each photon in "a" falls. The number
of boundaries might be ~40, so there will be 40^3=64000
cells to which the exiting photons might be assigned.
I would be inclined to use J's key adverb to perform your sums.
If I understand your description correctly, I think I would use:
sums=: (|:b) +//. a
bins=: ~.&.|: b
I would also think about replacing b with its transpose since
using it as a key suggests that would be more natural. Perhaps
using an expression like:
b=. (f0 I. a0),.(f1 I. a1),.(f2 I. a2)
--
Raul
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