That was very helpful, thanks!
But how to get rid of nested if-s?
If cond1 do
Something1
Else
If cond2 do
Something2
Else
Something3
End
End
Is there any rule of thumb for this case or is the approach everytime
depending on the specifics of the case?
Kairit Sirts
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:programming-
> [EMAIL PROTECTED] On Behalf Of Devon McCormick
> Sent: Friday, January 18, 2008 10:16 PM
> To: Programming forum
> Subject: Re: [Jprogramming] loopless code
>
> Kairit -
>
> as a rule, in J, you should be suspicious of any loop and ask the
> question:
> am I doing something here that is intrinsically serial?
>
> In the example above, it seems evident to me the answer is no. Then
> again,
> I've been doing this sort of thing for longer than the lifetime of the
> average beagle, so YMMV.
>
> To summarize what the first loop accomplishes: keep subtracting successive
> elements of the row (from a random number) until we get to or below zero.
> So, to turn this around and state more simply: where is the cumulative
> sum
> of the row greater than some arbitrary value? That is,
> index=. (roll>+/\row) i. 0
> gives the same index calculated by the loop.
>
> The latter part of this code, we want to make the index one if it's zero
> but
> leave it alone otherwise, or
> index=. 1>.index NB. Whichever is greater, one or the existing value
> (since we know index >:0)
>
> So, the two loops become the simple expression
> 1>.0 i.~roll>+/\row
> and "roll" is calculated from "row" but used only once so there's no point
> assigning it a name, so this becomes
> 1>.0i.~(?+/row)>+/\row
>
> Presumably you want to do this to all the rows. One way to do this is to
> fashion the statement above into a function
> rowWork=: 13 : '1>.0 i.~(?+/y)>+/\y'
> then apply this to each row of y:
> rowWork"1 y
>
> Hope you find this helpful.
>
> On 1/18/08, Kairit Sirts <[EMAIL PROTECTED]> wrote:
> >
> > >
> > > In fact, I think it would be a fruitful discussion to compare and
> > contrast
> > > the cases where we use:
> > >
> > > * "
> > > * /
> > > * ^:iteration_calculator
> > > * ^:condition^:_
> > > * $:
> > > * for. and while.
> > >
> > > I say that because I struggled with the third sentence of this
> > message. I
> > > couldn't quite articulate the type of problem which would cause one to
> > use
> > > $: instead of ^: .
> > >
> > > -Dan
> >
> > I myself am far too incompetent to start this fruitful discussion, but
> > actually I do have several peaces of code which are implemented with for
> > or
> > while loops. I don't like them and I'm quite sure there are nicer ways
> to
> > write them, but it has been to complicated to me so far.
> >
> > For example the following peace:
> >
> > y is a matrix of shape n * n
> > x is a number between 0..n-1
> >
> > roll =. ?+/ row =. x { y
> > index =. 0
> > while. roll > 0 do.
> > roll. =. roll. - index { row
> > index =: >: index
> > end.
> > if. index = 0 do.
> > index =. 1
> > end.
> >
> > For the last if-clause I figured out something like this:
> >
> > check =: =&0^:(=&0)
> >
> > And 'check index' seems to work as expected, but I'm not quite sure if
> it
> > really is working correctly
> >
> > Kairit Sirts
> >
> >
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
>
>
>
> --
> Devon McCormick, CFA
> ^me^ at acm.
> org is my
> preferred e-mail
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
----------------------------------------------------------------------
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