[Jprogramming] selection from a cube

[Henry Rich]

(<f;g;h) { y is the natural idiom, as Bob says here.

The implementation does the indexing two axes at a time, so that this is 
executed just like

h {"2 (<f;g) { y

Henry Rich

On 5/24/2020 12:17 PM, 'robert therriault' via Programming wrote:
> Hi Bill and Pascal,
>
> I'd use
>
>      (<f;g;h){ i. 5 4 3
> 56 54 55
> 59 57 58
> 50 48 49
> 53 51 52
>
> 20 18 19
> 23 21 22
> 14 12 13
> 17 15 16
>
> 44 42 43
> 47 45 46
> 38 36 37
> 41 39 40
>
> 32 30 31
> 35 33 34
> 26 24 25
> 29 27 28
>
>   8  6  7
> 11  9 10
>   2  0  1
>   5  3  4
>      1000 timespacex 'f{0 1|: g{ 0 1|: h{ 0 1|:a'
> 2.141e_6 9600
>     1000 timespacex '4 1 3 2 0 { 2 3 0 1 {("2) 2 0 1{"1 i.5 4 3'
> 1.568e_6 7104
>     1000 timespacex '(<f;g;h){ i. 5 4 3'
> 1.203e_6 5760
>     
> Cheers, bob
>
>> On May 24, 2020, at 08:40, 'Pascal Jasmin' via Programming <programming at jsoftware.com> wrote:
>>
>> don't know if any faster, but
>>
>>   4 1 3 2 0 { 2 3 0 1 {("2) 2 0 1{"1 i.5 4 3
>>
>>
>>
>>
>>
>>
>> On Sunday, May 24, 2020, 11:35:01 a.m. EDT, bill lam <bbill.lam at gmail.com> wrote:
>>
>>
>>
>>
>>
>> Suppose a I got a cube and selection vectors for each of the 3 axis, The
>> following is the way that I do the selection, to transpose the axis to the
>> front and then do selection. But I think this method is inefficient because
>> it transpose 3 times.  Any idea of better ways?
>>
>>    ]a=. i.5 4 3
>> 0  1  2
>> 3  4  5
>> 6  7  8
>> 9 10 11
>>
>> 12 13 14
>> 15 16 17
>> 18 19 20
>> 21 22 23
>>
>> 24 25 26
>> 27 28 29
>> 30 31 32
>> 33 34 35
>>
>> 36 37 38
>> 39 40 41
>> 42 43 44
>> 45 46 47
>>
>> 48 49 50
>> 51 52 53
>> 54 55 56
>> 57 58 59
>>
>>    f=.?.~5 [ g=.?.~4 [ h=. 2 0 1
>>    f;g;h
>> +---------+-------+-----+
>> |4 1 3 2 0|2 3 0 1|2 0 1|
>> +---------+-------+-----+
>>    f{0 1|: g{ 0 1|: h{ 0 1|:a
>> 56 54 55
>> 59 57 58
>> 50 48 49
>> 53 51 52
>>
>> 20 18 19
>> 23 21 22
>> 14 12 13
>> 17 15 16
>>
>> 44 42 43
>> 47 45 46
>> 38 36 37
>> 41 39 40
>>
>> 32 30 31
>> 35 33 34
>> 26 24 25
>> 29 27 28
>>
>> 8  6  7
>> 11  9 10
>> 2  0  1
>> 5  3  4
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