Or simply working directly with the table,
a conjunction can be defined that will generate
a verb on the fly for each set of index/values.
]DAT=: (<'McGuire')(0 4;2 4)}(<'Tom')(1 2;2 2)}":&.>i.4 5
+--+--+---+--+-------+
|0 |1 |2 |3 |McGuire|
+--+--+---+--+-------+
|5 |6 |Tom|8 |9 |
+--+--+---+--+-------+
|10|11|Tom|13|McGuire|
+--+--+---+--+-------+
|15|16|17 |18|19 |
+--+--+---+--+-------+
Test=: 2 : 'm ="0 1 n {"0 1/ ]'
('Tom';'McGuire') Test 2 4
(<;._1 ' Tom McGuire') (="0 1) 2 4 {"0 1/ ]
('Tom';'McGuire') Test 2 4 DAT
0 1 1 0
1 0 1 0
DAT #~ +./ ('Tom';'McGuire') Test 2 4 DAT
+--+--+---+--+-------+
|0 |1 |2 |3 |McGuire|
+--+--+---+--+-------+
|5 |6 |Tom|8 |9 |
+--+--+---+--+-------+
|10|11|Tom|13|McGuire|
+--+--+---+--+-------+
DAT #~ *./ ('Tom';'McGuire') Test 2 4 DAT
+--+--+---+--+-------+
|10|11|Tom|13|McGuire|
+--+--+---+--+-------+
--- Roger Hui <[EMAIL PROTECTED]> wrote:
> See http://www.jsoftware.com/jwiki/Essays/Inverted_Table
> If your data is appropriately organized as an inverted table
> you should be able to do
>
> (<(2 4{dat) tmemberof ,:&.>'Tom';'McGuire') #&.> dat
>
> Setting up the search target requires some care.
> You need to ensure that each opened item is a
> matrix (thus the ,:&.>) and that each opened item
> has the correct number of character columns
> (not shown above).
>
> Once you have done this, you can define a dyad
> whose left argument is the DB ("dat") and whose
> right argument are the target values, with a:
> indicating "don't care". e.g.
>
> where=: dyad define
> x #&.>~ <x tmemberof&((a: I.@:~: y)&{) y
> )
>
> dat where a:,a:,(<,:'Tom '),a:,(<,:'McGuire '),a:, ...
>
>
>
> ----- Original Message -----
> From: The World <[EMAIL PROTECTED]>
> Date: Tuesday, March 4, 2008 9:04
> Subject: [Jgeneral] best practice for argument handling
> To: General forum <[email protected]>
>
> > I want to pull all rows from a boxed table that I've created in
> > J, based
> > on specific values in certain columns. This is similar
> > to using WHERE <colvalue> = <value> to formulate SQL
> > queries. In J I
> > can do this by hand using standard J operators. Now I would like
> > to pull
> > it into a dyadic verb but I'm having trouble deciding the most
> > common
> > way to formulate the arguments. The y value is easy it will the
> > variable
> > that holds the table data (in this case I call it "dat"). But
> > now having
> > used my y argument I now need to stuff into the x argument the
> > column
> > numbers I want to base selection from and the strings that will
> > be used
> > to test for equality. Just so you get a feeling for what I'm
> > trying to
> > do the by hand formulation is as follows:
> >
> > ((2 }"1 dat) = <, 'Tom') *. (4}"1 dat) = <, 'McGuie'
> >
> > The above giving me a boolean array where the ones
> > represent the rows
> > where col 2 = Tom and Col4 =McGuire. Then I can just apply
> > the answer
> > with copy (#) to give me a new array with just those rows that
> > are
> > equal in col2 and col4.
> >
> > So is there a better way to organize this? Do you make the table
> > "dat"
> > global freeing up the y argument? I can certainly brute force
> > this but
> > I'm hoping for a more elegant solution that will be applicable
> > to future
> > problem spaces.
> >
> > Tom McGuire
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
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