Note that
c}b,:a
does indeed compute b,:a. But if it's used in the precise form
result =: c}b,:a
the computation is avoided.
b =: 1e6$4
a =: 1e6$4
c=: ? 1e6$ 2
ts 'c}b,:a'
0.0401299 2.09725e7
ts 'q =: c}b,:a'
0.0112949 4.19558e6
There are other special cases; see the Special Code page.
Henry Rich
On 12/21/2011 11:43 AM, Marshall Lochbaum wrote:
> A more obvious way is to use (c { b,.a) . The key is to realize that saying
> (if c then a else b) is just selection: if c is 0, we pick b, and if c is
> 1, we pick a. So we rephrase as (c { b,a), and J's implicit rank allows us
> to do (c { b,.a) for vector c, a, and b.
>
> That said, (c} b,:a) is faster, and uses less memory by not actually
> computing b,:a . So it's a better choice.
>
> Marshall
>
> On Wed, Dec 21, 2011 at 10:26 AM, Brian Schott<[email protected]>wrote:
>
>> One way is the following.
>>
>> c}b,:a
>> 10 2 30
>>
>>
>> --
>> (B=)
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>>
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