Yes this appears to be what I need.
I think in APL I used / in this way but for some reason
1 0 1 0 1 / 'abcde'
|domain error
| 1 0 1 0 1/'abcde'
1 0 1 0 1 / 'abcde'
|domain error
| 1 0 1 0 1/'abcde'
1 0 1 0 1 / 'abcde'
|domain error
| 1 0 1 0 1/'abcde'
1 1 0 0 1/i. 5
|domain error
| 1 1 0 0 1/i.5
1 1 0 1 1# 'abcde'
abde
1 0 1 0 1# i. 5
0 2 4
If there is a hint about this in the Volcabulary, somehow I missed
it. I expected that to be the easiest place to find out what a
particular symbol as used for but apparently not--here is the entry:
# Tally • Copy
#. Base 2 • Base
#: Antibase 2 • Antibase
If the arguments have an equal number of items, then x#y copies +/x
items from y, with i{x repetitions of item i{y . Otherwise, if one is
an atom it is repeated to make the item count of the arguments equal.
The complex left argument a j. b copies a items followed by b fills.
The fit conjunction provides specified fills, as in #!.f .
I believe there is probably a good reason why J does not map this
function to the verb / and does map it to # but right now I cannot
tell what that reason would be. If someone knows and would like to
enlighten me I would appreciate it and feel free to mock me for being
so dense while you are about it.
Thanks
Donna
On Sat 7/Oct/2006, at 7:38 PM, Dan Bron wrote:
I don't know what you mean, but filtering and selection can be
accomplished in many ways in J. The most fundamental, in my
opinion, is # . To wit:
] some_numbers =. 5 ? 10
2 7 1 9 5
greater_than_4 =. 4 < ]
] mask =. greater_than_4 some_numbers
0 1 0 1 1
mask # some_numbers
7 9 5
(#~ 4 < ]) some_numbers
7 9 5
Here, mask was a boolean list which indicated which elements of
some_numbers to keep and which to discard. That is, told #
which elements to filter.
My mnemonic for was (when I started), that # looks like a little
net or sieve. When you put things in a net, you lose whatever
lies over a hole, and you keep everything else. In a boolean list,
the 0s (little circles, absences) are the holes, and the 1s
the lines (presences), which together make up the net.
-Dan
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