R语言实战实现基于用户的简单的推荐系统（数量较少）
a<-c(1,1,1,1,2,2,2,2,3,3,3,4,4,4,5,5,5,5,6,6,7,7)
b<-c(1,2,3,4,2,3,4,5,4,1,2,3,2,4,5,2,6,4,1,2,3,4)
da<-data.frame(a,b)
a<-c(1,1,2,2,3,3,3,3,3,4,4,5,5,5,6,6,7,7)
b<-c(2,5,7,2,6,4,7,1,8,6,3,3,4,1,2,4,4,9)
da2<-data.frame(a,b)
ax<-unique(da$a)
bx<-unique(da$b)
m<-matrix(0,max(ax),max(ax))
for(i in 1:max(ax))
{
for(j in 1:max(ax))
{
if(i==j)
{
m[i,j]=0
}else{
m[i,j]=length(intersect(t(da[which(da$a==i),][2]),t(da[which(da$a==j),][2])))
}
}
}
m
myfun<-function(da,k,da2,m)
{
uid<-unique(c)
pre=0
recall=0
for (mm in 1:max(uid))
{
aa<-which(rank(-m[mm,])<k)
bb<-unique(da[unlist(lapply(da$a,function(x){
length(intersect(x,aa))!=0
})),][2])
movie<-setdiff(t(bb),t((da[which(da$a==mm),][2])))
movie2<-t(da2[da2$a==mm,][2])
p<-length(intersect(movie,movie2))/length(movie)
r<-length(intersect(movie,movie2))/length(movie2)
pre<-pre+p
recall<-recall+r
datafr[i,1]=k
datafr[i,2]=p
datafr[i,3]=r
if(mm==1)
{
user_top1<-which(rank(-m[mm,])<k)
movie_top2<-sort(movie[rank(movie)<k])
print(user_top1)
print(movie_top2)
}
}
preA<-pre/length(uid);
recallA<-recall/length(uid);
dataframe<-data.frame(c(k),preA,recallA)
return(dataframe)
}
df<-myfun(da,4,da2,m);
preA<-c()
recallA<-c()
k<-c()
daa<-data.frame(k,preA,recallA)
for(i in 3:7)
{
df<-myfun(da,i,da2,m);
daa<-rbind(daa,df)
}
daa
library(ggplot2)
qplot(preA,recallA,data=daa ,geom = c("point", "smooth"))
preA<-c()recallA<-c()k<-c()daa<-data.frame(k,preA,recallA)
原文：http://www.cnblogs.com/yjd_hycf_space/p/6718559.html