On Sat, Oct 22, 2016 at 3:05 PM, <meino.cra...@gmx.de> wrote: > Robby Findler <ro...@eecs.northwestern.edu> [16-10-22 21:28]: >> You need to follow the design recipe to solve a problem like this. You >> data is clear: [Listof [Listof Real]] and [Listof Real]. Next up: >> examples. Do you have examples of the inputs and outputs you want for >> this function? >> >> Robby >> >> On Sat, Oct 22, 2016 at 2:03 PM, <meino.cra...@gmx.de> wrote: >> > Hi, >> > >> > (I am still a newbie ... ) >> > >> > If I remember one rule of functional programming >> > correctly, it says: >> > Instead of changeing data - create new data. >> > >> > Suppose I have a list of list. Each "sublist" is >> > made of a greater amount (but identical count) of >> > exact numbers (integers). >> > >> > I want to process these data recursively and if >> > all is done I want to get back a list of numbers >> > (same count of numbers as in each sublist), which >> > represents the maximum of all numbers of that "position" >> > in all sublists. >> > >> > If I want to make this purely (may be inpractical) functional,.. >> > I see (as a newbie) the following problem. >> > From two numbers as input I have to build a maximum and >> > have to feed that into the next circle of recursion as >> > one of the numbers to compare. >> > Each time a new maximum is found I have to overwrite the >> > old one. >> > This contradicts the rule "Dont change data, create new one." >> > >> > How can I get out of this? >> > >> > Cheers >> > Meino >> > >> > >> > >> > >> > -- >> > You received this message because you are subscribed to the Google Groups >> > "Racket Users" group. >> > To unsubscribe from this group and stop receiving emails from it, send an >> > email to racket-users+unsubscr...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > Hi Robby, hi Phillip, hi Justin, > > thanks a lot for your help... !!! :) > This gives me mind twisters (but this was one reason > for me to learn racket ;) > > So, I think my "knot in the logic" was > to process one sublist at each circle of recursion > and being urged to create a temporary maximum with > each recursion that way, which gets possibly overwritten > in the next circle with a new temporary maximum. > > The 'apply map' creates - as far as I can understand it - > the maximum from ALL numbers of a certain position of all sublists > in one go. It creates on ONE maximum and no temporary resuls. > That's clever :) > > Cheers, > Meino > > From the Dictionary of Adanced Programming: > "Recursion, the: (see "Recursion" ) > >
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