if i.0 return 0

[Pascal Jasmin]

what is best way to test for "null" and if null return 0

f 3  NB. any non null at all, return y
3

f i.0
0

+/ works for scalars.

[robert therriault]

Hey Pascal,

I would guess that there are more elegant ways to approach this, but this is what I came up with.


s1=: 0:`]@.(*@#) NB. test for no items
s2=: 0:`]@.(0 -.@e. $) NB. test for empty array

s1 i. 2 3
0 1 2
3 4 5
s2 i. 2 3
0 1 2
3 4 5
s1 i. 0
0
s2 i. 0
0
s1 3 0 $ 5 NB. returns arg if it has items



s2 3 0 $ 5 NB. returns 0 if array is empty
0

Cheers, bob

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[Pascal Jasmin]

very nice.  s2 seems the most resilient.

for null or vector situations,

0 (0: :: {) y

can zero out any missing "expected" vector elements with x cycling through possibly expected vector indices.

[bill lam]

this should work for both array and scalar
*/@$

[Raul Miller]

I think by "null" you mean an array with an empty dimension?

If so, maybe

f=: {.~ 1 >. $

--
Raul

[Henry Rich]

Good solutions, but if you're putting them into a library consider:

1. ^:v is very fast, much faster than @.v

2.
https://code.jsoftware.com/wiki/Vocabulary/SpecialCombinations#Whole-Array_Operations
gives the best forms to test for empty etc.

Using that you get

s1 =: 0:^:(0=#)
s2 =: 0:^:(0 e. $)

As you show, the spec is defective.  What does 'null' mean?  You give
answers for the 2 most plausible definitions.

Henry Rich

[robert therriault]

I find your solutions more readable as well Henry. Simple "if true then 0 else original argument" construct.

Cheers, bob