I have a simple dataframe with two columns:

df <- data.frame(x = c(1,1,2,2,3), 
                 y = c(rep(1:2,2),1), 
                 target = c('a','a','a','b','a'))

I would like to compare the strings in the target column (find out whether they are equal or not, i.e., TRUE or FALSE) within every level of x (same number for x). First I would like to compare lines 1 and 2, then 3 and 4 ... My problem is that I am missing some comparisons, for example, line 5 has only one case instead of two - so it should turn out to be FALSE. Variable y indicates the first and second case within x.

I played around with ddply doing something like:

ddply(df, .(x), summarise,
        ifelse(as.character(df[df$y == '1',]$target), 
               as.character(df[df$y == '2',]$target),0,1))

which is ugly ... and does not work ...

Any insights how I could achieve this comparison?

Thanks