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
----------------------------------------------------------------------
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