PG=Paul Gauthier, DB=me
DB> 'gree' dbp g
DB> 1 7
DB> 2 9
PG> It should be:
PG> 1 7
PG> 2 0
Yes, you're right. I changed the noun g to fit better into one line of an
email message, but I didn't re-execute the snippet
that'd I'd already copied into the email. Indeed, when run in a fresh J
session:
idx0 =. $ #: I.@:,
ptrn =. E.&>/@:((>. - ,)&:(#@:$) ,:@:]^:[&.> ,&:<)
dbp =. idx0@:ptrn
g =._3;:^:_1\;:'the grass is always greener when greecian grown'
'gree' dbp g
1 7
2 0
Sorry about that.
> And I can't figure out the reason behind the fancier ptrn ?
The fancier ptrn allows you to locate an rectangle of arbitrary rank in an
array of greater or equal rank. It's not restricted to
rank-1 arrays.
But I believe you're right, that with the proper n in x E."n y the
expression would equivalent to x ptrn y . The problem is
that dynamic ranks can't be tacit. Plus part of the point of the message was
to advertise the idiom ,:^(difference in rank) .
To wit:
rank =: #@:$
makeRank2 =: ,:^:(2 - rank)
rank makeRank2 scalar =. 2
2
rank makeRank2 vector =. i. 2
2
rank makeRank2 table =. i. 2 2
2
rank makeRank2 cube =. i. 2 2 2
2
rank makeRank2 hcube =. i. 2 2 2 2
2
-Dan
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