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{ Improved

initial writing: 2000-10-20 last updated: 2004-10-26

The case (<i;j;k; ...){y where leading indices are singleton integer arrays, is now implemented by special code. Some benchmarks:

   ts=: 6!:2 , 7!:2@]  NB. time and space

   a=: ?. 2 3 4 1e5$1e9   [ i=: <(?.&.>2 3 4),<?.4 5$1e5
   b=: o.?.40 2 15000$1e6 [ j=: <20;0;_4
   c=: ?. s$1e9           [ k=: <?.&.>$s=:13 11 7 5 3 2

Expr.	J 4.06		J 4.05
i{a	2.54222e_5	1408	1.12953e_2	2098560
j{b	2.29079e_5	1088	7.09867e_4	132352
k{c	1.88292e_4	17216	6.64889e_5	17408

Also, the dyad { for Boolean left arguments is now implemented by special code. Some benchmarks:

   b=: ?.1e6$2
   x=: (2,c)$'abcdefghijqrstuvwxyz'
   ts 'b{x'

c	J 4.06	J 4.05	Time Ratio
1	0.0217949 1.049280e6	0.1060300 9.438080e6	4.86
2	0.0227065 2.097856e6	0.1074530 1.048666e7	4.73
3	0.0390362 4.195008e6	0.1726359 1.258381e7	4.42
4	0.0283271 4.195008e6	0.1164168 1.258381e7	4.11
5	0.0456212 8.389824e6	0.1772309 1.677811e7	3.88
6	0.0446817 8.389824e6	0.1964577 1.677811e7	4.40
7	0.0478795 8.389824e6	0.2010920 1.677811e7	4.20
8	0.0426456 8.389312e6	0.1538154 1.677811e7	3.61
9	0.0574534 1.677794e7	0.2152081 2.516672e7	3.75
10	0.0579359 1.677794e7	0.2198388 2.516672e7	3.79
11	0.0729431 1.677794e7	0.2220768 2.516672e7	3.04
12	0.0833206 1.677794e7	0.2088402 2.516672e7	2.51
30	0.1592722 3.355718e7	0.2551766 4.194394e7	1.60

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