J does not have a primitive verb which permutes values of atoms, like C.
permutes indexes.
So, if P would be such a primitive, then (5 0 3; 1 2) P y would replace in
y each 5 by 0, each 0 by 3 and each 3 by 5 and swap 1's and 2's.
Contrary to the behaviour of C. , preferably P accepts only boxed left hand
argument.
One way to realize P with the use of C. is:
P=: [EMAIL PROTECTED] $ (((i.!.0~ ~.)@] { (((i.&.>~<) C. ]) ~.)) ,)
a ; (5 0 3;1 2) P a =: 3 4 [EMAIL PROTECTED]
+---------+---------+
|0 5 5 4 2|3 0 0 4 1|
|3 2 1 4 2|5 1 2 4 1|
|0 2 1 4 1|3 1 2 4 2|
|2 4 0 4 0|1 4 3 4 3|
| | |
|5 4 0 0 0|0 4 3 3 3|
|5 1 5 0 4|0 2 0 3 4|
|5 5 2 0 0|0 0 1 3 3|
|1 1 5 3 1|2 2 0 5 2|
| | |
|3 2 1 1 3|5 1 2 2 5|
|4 4 3 5 5|4 4 5 0 0|
|5 0 1 0 3|0 3 2 3 5|
|1 3 5 0 1|2 5 0 3 2|
+---------+---------+
As can be seen, realizing P using C. can be rather complicated
On the other hand, it would be easy to realize C. with the help of P, as C.
is a special case of P, applying P to the array of indexes.
C. would be (roughly) equal to (P [EMAIL PROTECTED]) { ]
(5 0 3;1 2) ((P [EMAIL PROTECTED]) { ]) 'ABCDEF'
DCBFEA
The conclusion seems to be that P is more primitive than C.
What is the opinion of the forum on this?
R.E. Boss
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