Code example for first 10 odd numbers on APL is incorrect

codereport / jsource

J Language Source Code. Livestream links ⬇️

https://www.youtube.com/playlist?list=PLVFrD1dmDdvfVhYLU_iKkV67X9XqCJLWe

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Code example for first 10 odd numbers on APL is incorrect #206

Closed herwinw closed 3 years ago

herwinw commented 3 years ago

It looks like ⍳ in APL starts at 1 instead of 0, the code snippet linked in the readme generates the sequence, 3, 5 .. 21

juntuu commented 3 years ago

I think it just assumes index origin to be set to zero.

      ⎕IO←0
      ⍳4
0 1 2 3

herwinw commented 3 years ago

I tried the Runnable link from the README, that iota is 1-indexed for me. I'm not sure whether that's a global default, or it saves something in cookies which causes the result to differ depending on that.

juntuu commented 3 years ago

Since TryAPL has index origin 1 by default, some possible fixes would be:

Subtract one instead of adding (as the R sample does)
```
¯1+2×⍳10
```
or set the index origin to zero first in the linked snippet (the sharable link unfortunately needs to fit on one line)
```
⎕IO←0 ⋄ 1+2×⍳10
1+2×⍳10 ⊣ ⎕IO←0
```

codereport commented 3 years ago

We decided to go with ¯1+2×⍳10. Thanks for pointing this out.