To define a relational join, there need to be
an agreement on what columns are matched,
and what are selected.
Suppose, A and B are lists of tupples with attributes
in columns.
A (ia;ib;sa;sb) join B
will return list of tuples, where column ia of A
matches ib of B, with attributes sa from A and sb from B.
jndx=: (0 , [EMAIL PROTECTED]) #: [: I.@, =/ NB. join indices
join=: 1 : 0 NB. A (ia;ib;sa;sb) join B
:
'ia ib sa sb'=. m
'ja jb'=. |:(ia {"1 x) jndx ib {"1 y
(sa {"1 ja { x) ,. sb {"1 jb { y
)
Examples
A=. 1 101,2 102,3 103,:5 104
B=. 1 201,3 202,1 203,2 204,4 205,:3 206
A;B
+-----+-----+
|1 101|1 201|
|2 102|3 202|
|3 103|1 203|
|5 104|2 204|
| |4 205|
| |3 206|
+-----+-----+
A 0 0 1 1 join B
101 201
101 203
102 204
103 202
103 206
X =. 15 3 $ 12 | 45 ?. 200
Y =. 10 4 $ 12 | 40 ?. 60
X;Y
+--------+----------+
| 2 6 7| 6 11 1 10|
| 7 6 5|10 8 8 1|
| 8 6 0| 5 11 8 8|
| 4 2 4| 2 0 1 5|
| 9 4 9|10 11 4 3|
| 8 10 5| 7 7 0 5|
| 6 11 7| 0 0 9 3|
| 7 10 5|10 4 3 7|
| 4 11 3| 4 9 5 8|
| 2 1 9| 7 1 3 3|
| 9 2 4| |
|11 8 6| |
|11 0 1| |
| 0 5 10| |
| 5 10 11| |
+--------+----------+
X (0;0;0 1 2;0 1 2 3) join Y
2 6 7 2 0 1 5
7 6 5 7 7 0 5
7 6 5 7 1 3 3
4 2 4 4 9 5 8
6 11 7 6 11 1 10
7 10 5 7 7 0 5
7 10 5 7 1 3 3
4 11 3 4 9 5 8
2 1 9 2 0 1 5
0 5 10 0 0 9 3
5 10 11 5 11 8 8
--- Yuvaraj Athur Raghuvir <[EMAIL PROTECTED]> wrote:
> Pacal, the solution proposed has a problem as it does not scale right.
> Looks like there is an assumption on the shape somewhere.
>
> Let me call the rajoin you have proposed as rajoin1.
>
> rajoin1 =: 4 : '(x ,. ]) (({: |: x) i.~ ({. |: y)) { {: |: y'
>
> Now, try this:
> x =. 15 3 $ 12 | 45 ?. 200
> y =. 10 4 $ 12 | 40 ?. 60
>
> x rajoin1 y
> |index error: rajoin1
> | (x,.])(({:|:x)i.~({.|:y)) {{:|:y
>
> However,
> x rajoin y
> +----+--+-------+
> |2 6 |7 |7 0 5 |
> +----+--+-------+
> |2 6 |7 |1 3 3 |
> +----+--+-------+
> |7 6 |5 |11 8 8 |
> +----+--+-------+
> |8 6 |0 |0 9 3 |
> +----+--+-------+
> |4 2 |4 |9 5 8 |
> +----+--+-------+
> |8 10|5 |11 8 8 |
> +----+--+-------+
> |6 11|7 |7 0 5 |
> +----+--+-------+
> |6 11|7 |1 3 3 |
> +----+--+-------+
> |7 10|5 |11 8 8 |
> +----+--+-------+
> |9 2 |4 |9 5 8 |
> +----+--+-------+
> |11 8|6 |11 1 10|
> +----+--+-------+
> |0 5 |10|8 8 1 |
> +----+--+-------+
> |0 5 |10|11 4 3 |
> +----+--+-------+
> |0 5 |10|4 3 7 |
> +----+--+-------+
>
> ]x
> 2 6 7
> 7 6 5
> 8 6 0
> 4 2 4
> 9 4 9
> 8 10 5
> 6 11 7
> 7 10 5
> 4 11 3
> 2 1 9
> 9 2 4
> 11 8 6
> 11 0 1
> 0 5 10
> 5 10 11
> ]y
> 6 11 1 10
> 10 8 8 1
> 5 11 8 8
> 2 0 1 5
> 10 11 4 3
> 7 7 0 5
> 0 0 9 3
> 10 4 3 7
> 4 9 5 8
> 7 1 3 3
>
>
> On 10/23/06, Pascal Jasmin <[EMAIL PROTECTED]> wrote:
> > this will work if y is sorted (easily fixed if not) and indexed
> > continuously (left column)
> from 1 to #y
> >
> > (x ,. ]) (1 -~ {: |: x) { {: |: y
> >
> > otherwise, we need to make an indexlookup verb (just i.~) as the left
> > argument for { .
> >
> > (x ,. ]) (({: |: x) i.~ ({. |: y)) { {: |: y
> > rajoin =: 4 : '(x ,. ]) (({: |: x) i.~ ({. |: y)) { {: |: y'
> >
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
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