[R] make a shortlist of data based on blocks of binary values in one column

My question is twofold. Part 1: My data looks like this: (example set, real data has 2*10^6 rows) binary<-c(1,1,1,0,0,0,1,1,1,0,0) Chromosome<-c(1,1,1,1,1,1,2,2,2,2,2) start<-c(12,17,18,20,25,36,12,15,16,17,19) Table<-cbind(Chromosome,start,binary) Chromosome start binary [1,] 1

[R] 'Record' row values every time the binary value in a collumn changes

My question is twofold. Part 1: My data looks like this: (example set, real data has 2*10^6 rows) binary<-c(1,1,1,0,0,0,1,1,1,0,0) Chromosome<-c(1,1,1,1,1,1,2,2,2,2,2) start<-c(12,17,18,20,25,36,12,15,16,17,19) Table<-cbind(Chromosome,start,binary) Chromosome start binary [1,] 1