Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #25403

Re: General solution to get the previous value

Show all headers | View raw

Den onsdagen den 16:e juli 2014 kl. 16:23:41 UTC+2 skrev Scott Sauyet:
> jonas.thornvall@gmail.com wrote:
> 
> > number=29;
> 
> > basemultip=1;
> 
> > base=3;
> 
> > 
> 
> > while (basemultip < number)
> 
> >    {
> 
> >       prevmultip=basemultip;
> 
> >       basemultip = basemultip * base;
> 
> >      
> 
> >    }
> 
> > basemultip=prevbase;
> 
> > 
> 
> > What is the solution to have the previous value when you walk 
> 
> > out from loop, i think my code look strange and i probably 
> 
> > learned how to do this but forgot about it.
> 
> > 
> 
> > Can i do it without buffering the previous value?
> 
> 
> 
> Doing this in a function might help.  One approach:
> 
> 
> 
>     var findLast = function(base, number) {
> 
>       var current = 1;
> 
>       while (true) {
> 
>         next = base * current;
> 
>         if (next >= number) {return current;}
> 
>         current = next;
> 
>       }
> 
>     }
> 
> 
> 
>     findLast(3, 29); //=> 27
> 
> 
> 
> Note that this has no error checking.  You might want to check that 
> 
> your target is greater than 1, and that your base is greater than 1.
> 
> 
> 
> But note that this could easily be abstracted into a more general 
> 
> pattern, which might itself be useful:
> 
> 
> 
>     var findLast = function(start, getNext, predicate) {
> 
>       var current = start;
> 
>       while (true) {
> 
>         next = getNext(current);
> 
>         if (!predicate(next)) {return current;}
> 
>         current = next;
> 
>       }
> 
>     }
> 
> 
> 
>     var base = 3, number = 29;
> 
>     findLast(1, function(n) {return base * n;}, 
> 
>                 function(n) {return n < number;}); //=> 27
> 
> 
> 
> Again this is missing some error checking.  You might want to at 
> 
> least test that the initial value passes the predicate:
> 
> 
> 
>       if (!predicate(start)) {throw new Error('Illegal initial value');}
> 
> 
> 
> It would be harder in this general case though to ensure that we'll ever hit the termination condition.
> 
> 
> 
>   -- Scott

It seem to use two conditional checks, While(true) and if(predicate) but maybe it still faster by not buffering the value each loop?

I think it kind of weird that there seem to be no loop construction that could catch this case. 

Back to comp.lang.javascript | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

General solution to get the previous value jonas.thornvall@gmail.com - 2014-07-15 17:25 -0700
  Re: General solution to get the previous value jonas.thornvall@gmail.com - 2014-07-15 21:25 -0700
    Re: General solution to get the previous value Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-07-16 13:06 +0100
  Re: General solution to get the previous value Scott Sauyet <scott.sauyet@gmail.com> - 2014-07-16 07:23 -0700
    Re: General solution to get the previous value jonas.thornvall@gmail.com - 2014-07-16 07:58 -0700
      Re: General solution to get the previous value jonas.thornvall@gmail.com - 2014-07-16 13:35 -0700
    Re: General solution to get the previous value Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-07-16 17:05 +0100
      Re: General solution to get the previous value jonas.thornvall@gmail.com - 2014-07-16 11:07 -0700
      Re: General solution to get the previous value Scott Sauyet <scott.sauyet@gmail.com> - 2014-07-16 12:13 -0700
      Re: General solution to get the previous value "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-07-16 22:45 +0200

csiph-web