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{/: and {/:~ Improved |
initial writing: 2008-03-20 |
The dyads x{/:y and x{/:~y can be used to compute order statistics such as the median. They have been made more efficient for integer atom x and integer or floating-point list y . The following benchmarks demonstrate the improvements.
x=: ?1e6 i=: 1e6 ?@$ 2e9 d=: 0.01 * i ts=: 6!:2 , 7!:2@] NB. time and space 100 ts 'Expression'
| Expression | J 7.01 | J 6.02 | Ratio | |||||||||
| x ({/: ) i | 0.028988 | 2.09856e6 | 0.214498 | 8.91366e6 | 7.40 | 4.25 | ||||||
| x ({/:~) i | 0.027497 | 4.19584e6 | 0.137272 | 8.91386e6 | 4.99 | 2.12 | ||||||
| x ({/: ) d | 0.045599 | 4.19571e6 | 0.340021 | 8.91366e6 | 7.46 | 2.12 | ||||||
| x ({/:~) d | 0.046481 | 4.19584e6 | 0.161224 | 1.73025e7 | 3.47 | 4.12 | ||||||