I need a simple utility that will return the numeric value represented by
a string y, following the rules of dyadic ". except returning the scalar x
if y is empty. This should be fast since it is to be applied under > to
large arrays of boxed strings whose exact format cannot be controlled. I
have observed that if y is preceded by a TAB the result of ". is
unchanged, and if y is a TAB alone the result is x; therefore adding a TAB
before (each) y seems to do the trick. But this is not documented in the
Vocabulary. Can I trust this behaviour to continue in future editions of
J?
Adding a space would seem more natural but ". treats y that is all spaces
like an empty vector. Best would be if the left argument to ". had an
optional second element, specifying the exact number of elements to be
returned in each row, or default 0 for the present behaviour. Then I
could force an empty y to receive the padding value 0{x.
Thanks,
Richard Vaughan
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