Thanks Brian - this looks like it solve it. I will study it to get a better understanding of how to solve problems like this. Thanks for adding comments too. It makes the steps more clear.
On Tue, Aug 27, 2013 at 8:55 AM, Brian Schott <[email protected]>wrote: > freqcount=: (\: {:"1)@(~. ,. #/.~) > CT =: 100 > picks =: CT ?.@$ 26 > groups =: CT $ i. 3 > f =: groups <@freqcount/. picks NB. freqcounts of picks > g =:; (i. 3) ((|.&.|:)@>@]<@:,.[)"0 f NB. appending group #s > s =: \:~ g NB. sorting > r =: (i.26) ((0,~])\:~@{~1&{"1@]i./ [)s NB. remove duplicates > t =: |.({:"1@]</.])\:~&.(|.&.|:) r NB. rearrange > 3&{. each t NB. first 3 > > The above may be a solution, but is not well tested. Instead of movie > names, there are movie numbers. > > > > > > > On Mon, Aug 26, 2013 at 11:22 PM, Joe Bogner <[email protected]> wrote: > > > I solved this problem today at work in R using a loop and an intermediate > > data.table. I generalized it and then tried to solve it in J. I wasn't > even > > sure where to start. > > > > Let's say you have 100 students and 26 movies that need to be shared by 3 > > groups of students. Each student has picked their favorite movie. I need > to > > give 3 movies to each of the 3 groups based on the group's favorite > > choices. A movie can't be shared by groups. > > > > > > movies=:(65 + i. 26) { a. > > > > CT=:100 > > > > > > NB. movie;student;age group > > > > students=:i.CT > > > > groups=:(CT $ (i.3)) > > > > picks=: ((?. CT $ # movies) { movies);students;groups > > > > > > NB. get an idea of what the most common choices are across all groups > > > > key=. > 0{"1 picks > > > > values=. CT $ 1 > > > > sum=: +/ > > > > counts=. (~.key) ; (i.~key) sum/. values > > > > > > NB. sidenote how do I get this table format? > > > > NB. |-----|---| > > > > NB. |M | 1 | > > > > NB. |-----|---| > > > > NB. |W| 1 | > > > > > > > > Any advice on how to tackle this in J? > > > > > > This is the solution in R > > > > > > movies <- LETTERS > > > > CT <- 100 > > > > students <- rep(0:(CT-1)) > > > > groups <- sample(0:2,100,replace=T) > > > > picks <- data.table(data.frame(movie=sample(movies,100, > > replace=T),student=students, group=groups)) > > > > > > > > movie.groups <- picks[,.N,by=list(movie,group)] > > > > movie.groups[,Taken:=F] > > > > > > ugroups <- unique(groups) > > > > for(i in 1:length(ugroups)) { > > > > g<-ugroups[i] > > > > top3 <- movie.groups[group==g & Taken==F,][order(-N)][1:3] > > > > > > setkey(top3,movie,group) > > > > setkey(movie.groups,movie,group) > > > > movie.groups[top3, ForGroup:=T,nomatch=0] > > > > > > setkey(top3, movie) > > > > setkey(movie.groups,movie) > > > > movie.groups[top3, Taken:=T,nomatch=0] > > > > } > > > > > > > > >movie.groups[ForGroup==T,list(movie,group)][order(group)] > > > > movie group > > > > 1: P 0 > > > > 2: T 0 > > > > 3: W 0 > > > > 4: F 1 > > > > 5: H 1 > > > > 6: N 1 > > > > 7: D 2 > > > > 8: E 2 > > > > 9: K 2 > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > > -- > (B=) <-----my sig > Brian Schott > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
