library(magrittr)
library(data.table)
n_row = seq(1,1e7) %in% sample(1e7,1e5)

seq  <- rle(n_row)
idx  <- c(0, cumsum(seq$lengths))[which(seq$values)] + 1
indx <- data.frame(start=idx, length=seq$length[which(seq$values)])

result <- do.call(rbind,apply(indx,1, function(x) return(fread(file,nrows=x[2],skip=x[1],sep=','))))