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Re: sidetrack

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On Thursday, December 9, 2021 at 7:39:22 PM UTC-6, luserdroog wrote:
> On Wednesday, December 8, 2021 at 11:38:30 PM UTC-6, Michael Haufe (TNO) wrote: 
> > On Wednesday, December 8, 2021 at 6:23:12 PM UTC-6, luser...@gmail.com wrote: 
> > > On Wednesday, December 8, 2021 at 6:17:07 PM UTC-6, luserdroog wrote: 
> > > 
> > > > function running_sum( a ){ 
> > > > var t = []; 
> > > > a.reduce( (pre,cur)=>{t.push(pre+cur),pre+cur} 
> > > , 0 
> > > > ); 
> > > > return t; 
> > > > } 
> > > > 
> > > > It's not a "one liner", but this is probably a bit more efficient AFAICT. 
> > > > In APL, it's just `+\`. 
> > > Need to use initial value zero (or prepend the original first element). 
> > > I really think that's right, now. 
> > functionally: 
> > 
> > const add = (left, right) => left + right 
> > 
> > const sum = (xs) => xs.reduce(add,0) 
> > 
> > sum([1,2,3,4,5]) // 15
> That does an APL reduce (coincidentally named) which looks like: 
> 
> +/ 
> 
> But I'm after the subtly different function does a "scan" or piece-wise 
> reduce. In APL, it's almost imperceptibly different: 
> 
> +\ 
> 
> (There's a joke that APL\360 was named with the backslash character 
> in there so the product name means "APL extends 360" if treated as 
> an APL program. \ means "extend" if the left and right are values, but 
> in the snippets under consideration \ means "scan" because the left 
> (+) is a function and not a value. I will endeavor to stop talking about 
> APL after this message.) 
> 
> To be more functional, I think it would look like this: 
> 
> Array.prototype.scan = function( f ){ 
> return this.map( (e,i,a)=>a.slice(0,i+1).reduce(f,0) ); 

dangitall.

> } 
> const add = (left,right) => left + right 
> 
> function running_sum( a ){ 
> return [ 0, ...a.scan( add )]; 
> } 
> 
> (I forgot I also needed the result of running_sum() to start with a zero, 
> in addition to the zero that gets fed to reduce() to ensure the first 
> element of the input array shows up in the output array.)

Erhm. We don't need that zero in reduce() anymore. The map() takes
care of that.

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sidetrack luserdroog <luser.droog@gmail.com> - 2021-12-07 18:42 -0800
  Re: sidetrack "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-12-08 13:03 -0800
    Re: sidetrack luserdroog <luser.droog@gmail.com> - 2021-12-08 16:17 -0800
      Re: sidetrack luserdroog <luser.droog@gmail.com> - 2021-12-08 16:23 -0800
        Re: sidetrack "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-12-08 21:38 -0800
          Re: sidetrack luserdroog <luser.droog@gmail.com> - 2021-12-09 17:39 -0800
            Re: sidetrack luserdroog <luser.droog@gmail.com> - 2021-12-09 17:44 -0800
            Re: sidetrack Scott Sauyet <scott@sauyet.com> - 2021-12-10 07:26 -0800
        Re: sidetrack Elhwen Dico <elhwen.dicote@gmail.com> - 2021-12-10 16:30 +0100
          Re: sidetrack Elhwen Dico <elhwen.dicote@gmail.com> - 2021-12-10 16:37 +0100
          Re: sidetrack Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-12-11 01:56 +0100
            Re: sidetrack Julio Di Egidio <julio@diegidio.name> - 2021-12-11 10:12 +0100
  Re: sidetrack luserdroog <luser.droog@gmail.com> - 2021-12-09 19:22 -0800

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