That sounds like a job for agenda:
collatz =: collatz_even`collatz_odd@.(2&|)
the expression to the right of the Agenda (@.) returns 0 or 1 for any
scalar integer input; that will be used to select one of the verbs to
the left to be executed,
On Mon, Mar 3, 2014 at 11:30 AM, Jon Hough <jgho...@outlook.com> wrote:
> Beginner question again.I quick task I set myself was to write ONE ITERATION
> of the Collatz function for a given positive
> integer.http://en.wikipedia.org/wiki/Collatz_conjecture
>
> So my verb is supposed to do 3*n+1 if n is odd and n/2 if n is even.In a more
> imperative/OOE based language (C/C++/Java) I could write this in less than a
> minute. Unfortunately, I fell at the very first hurdle in J.
> I originally wrote my tacit verb for even ints:collatz_even =.2&(%~)
> collatz_even 4
> 2
> This works, but I had a terrible time trying to put the brackets in the right
> place. I am not sure why %~ needs to be bracketed. Won't J parse %~ as dyadic
> and "know" that the left operand is 2?
> Next I tried to do the case for odd n:
> collatz_odd =. 1&+@(3&*) collatz_odd 3
> 10
> That seems to work ok.Now I am not sure how to do an if statement in J. In
> plain English I want "If n is even do collatz_even else do collatz_odd".The
> verb I wrote to test for even-ness is
> ones =. {:@#: NB. Finds the ones column values. 1 => odd, 0=> even
> 1 = ones 2
> 0
> So I have a test but I am not sure how to utilize this test. How should I go
> about doing:"If n is even do collatz_even else do collatz_odd"?
> Thanks and regards,Jon
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
--
- michael dykman
- mdyk...@gmail.com
May the Source be with you.
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