r - Merge data frames for Cohen's kappa -

i'm trying analyze date using r i'm not familiar r (yet) , therefore i'm totally stuck.

what try manipulate input data can use calculate cohen's kappa. problem is, rater_1, have several ratings of items , need select one. if rater_1 has given same rate on item rater_2, rating should chosen, if not rating of list can used.

i tried

unique(merge(rater_1, rater_2, all.x=true)) 

which brings me close, if ratings between 2 raters diverge, 1 kept.

so, question is, how from

item rating_1 1    3 2    5 3    4   item rating_2 1    2 1    3 2    4 2    1 2    2 3    4  3    2 

to

item rating_1 rating_2 1    3         3 2    5         4 3    4         4 

?

there fancy ways this, thought might helpful combine few basic techniques accomplish task. usually, in question, should include easy way generate data, this:

# create sample data set.seed(1) id<-rep(1:50) rater_1<-sample(1:5,50,replace=true) df1<-data.frame(id,rater_1)  id<-rep(1:50,each=2) rater_2<-sample(1:5,100,replace=true) df2<-data.frame(id,rater_2) 

now, here 1 simple technique doing this.

# merge data frames. all.merged<-merge(df1,df2) #   id rater_1 rater_2 # 1  1       2       3 # 2  1       2       5 # 3  2       2       3 # 4  2       2       2 # 5  3       3       1 # 6  3       3       1  # find ones equal. same.rating<-all.merged[all.merged$rater_2==all.merged$rater_1,] # consider id 44, match twice. # remove duplicates. same.rating<-same.rating[!duplicated(same.rating),] # find ones never matched. not.same.rating<-all.merged[!(all.merged$id %in% same.rating$id),] # pick one. chose pick maximum. picked.rating<-aggregate(rater_2~id+rater_1,not.same.rating,max) # stick 2 together. result<-rbind(same.rating,picked.rating) result<-result[order(result$id),] # sort  #     id rater_1 rater_2 # 27   1       2       5 # 4    2       2       2 # 33   3       3       1 # 44   4       5       3 # 281  5       2       4 # 11   6       5       5 

---

a fancy way this:

same.or.random<-function(x) {   matched<-which.min(x$rater_1==x$rater_2)   if(length(matched)>0) x[matched,]   else x[sample(1:nrow(x),1),] } do.call(rbind,by(merge(df1,df2),id,same.or.random))