I just read this thread of last October.
The following phrase based on Take is type independent, accepts
duplicates and fill elements. It does not "manipulate" data with
* or /: or move it around with $ . It also handles an empty argument.
Concise enough? a matter of compromise.
diagonal =: ( {."_1~ -@:>:@:i.@:# )
diagonal 99 1x1 0 _1j1 99
99 0 0 0 0
0 2.71828 0 0 0
0 0 0 0 0
0 0 0 _1j1 0
0 0 0 0 99
<diagonal 'a b c d ' NB. suitable for text-diamond 2009/04/17
+--------+
|a |
| |
| b |
| |
| c |
| |
| d |
| |
+--------+
diagonal (<s: ' tra'),<"0] 99 1x1 0 _1j1 99
+----+--+-------+-+----+--+
|`tra| | | | | |
+----+--+-------+-+----+--+
| |99| | | | |
+----+--+-------+-+----+--+
| | |2.71828| | | |
+----+--+-------+-+----+--+
| | | |0| | |
+----+--+-------+-+----+--+
| | | | |_1j1| |
+----+--+-------+-+----+--+
| | | | | |99|
+----+--+-------+-+----+--+
diagonal a:,3#<+`-
++-----+-----+-----+
|| | | |
++-----+-----+-----+
||+-+-+| | |
|||+|-|| | |
||+-+-+| | |
++-----+-----+-----+
|| |+-+-+| |
|| ||+|-|| |
|| |+-+-+| |
++-----+-----+-----+
|| | |+-+-+|
|| | ||+|-||
|| | |+-+-+|
++-----+-----+-----+
$diagonal ''
0 0
The lower triangle can be filled with a constant fill atom
(type dependent):
( {.!.'.'"_1~ -@:>:@:i.@:# )'abcdef'
a
.b
..c
...d
....e
.....f
or with a variable fill atom (but not tacitly in this form I think):
'*'( 4 : '(->:i.# y) {.!.x "_1 y' ) 'abcdef'
a
*b
**c
***d
****e
*****f
~ Gilles
---------- Original Message -----------
From: "Raul Miller" <[email protected]>
To: "Programming forum" <[email protected]>
Sent: Sat, 11 Oct 2008 14:40:18 -0400
Subject: [Jprogramming] diagonal arrays
> Given a vector, put it on the diagonal of an array:
>
> (<0 1)&|:inv 2 7 9 20
> |index error
> (+/ .*(e.(<0 1 2 )&|:)@i.@(3##)) 2 7 9 20
> 2 0 0 0
> 0 7 0 0
> 0 0 9 0
> 0 0 0 20
> (, $~ 2##)@(,"0 1*&0)2 7 9 20
> 2 0 0 0
> 0 7 0 0
> 0 0 9 0
> 0 0 0 20
>
> Are there more concise approaches, that work?
>
> Thanks,
>
> --
> Raul
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
------- End of Original Message -------
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