Has anyone considered implementing axis arguments for ⊥ and ⊤? It would
be nice if you could encode or decode on a chosen axis. For instance,
say that you have an 8-bit RGB image represented by an array of integers
of the shape height×width×3. The first two dimensions are the height and width of the image, the third dimension is 3 units long for the R G B
values.

If you want to count the unique colors in the image, you can do it with
this function:

countColors ← {⍴∪,(3⍴2*8)⊥3 1 2⍉⍵}

You have to permute the array to put the RGB dimension first in order
for the decode to work. What if you could write this instead:

countColors ← {⍴∪,(3⍴2*8)⊥[3]⍵}

Is there a reason this hasn't been implemented? For multidimensional
arguments, there could be a second axis argument to specify which
dimension of the left argument to use as radix vectors for the right
argument: A⊥[3;2]B.

Andrew

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Hi Andrew,

Might be rank operator would serve the purpose? Example in NARS2000:

+RGB←?3 4 4⍴256
213 135 171 165
131 111 105 81
43 63 133 231
162 102 196 168

233 65 43 216
74 136 222 119
54 206 117 149
78 71 27 95

50 181 190 129
220 71 62 248
58 19 13 231
32 154 34 118

{(3⍴2*8)(⊥⍤3)⍵}RGB
14018866 8864181 11217854 10868865
8604380 7309383 6938174 5339128
2831930 4181523 8746253 15177191
10636832 6703002 12852002 11034486


Observe that the first pixel has RGB value (213 233 50) and is encoded as 14018866 by above dfn like below:

256 256 256⊥213 233 50
14018866


Jim

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