Selecting top N rows for each group based on value in column

Question

I have dataframe like below :-

x<-c(3,2,1,8,7,11,10,9,7,5,4)
y<-c(\"a\",\"a\",\"a\", \"b\",\"b\",\"c\",\"c\",\"c\",\"c\",\"c\",\"c\")
z<-c(2,2,2,1,1         


        

Answer 1

One approach with data.table:

library(data.table)
setDT(df)
df[,.(inc=seq_len(.N)<=z,x,z),by=.(y)][inc==T ,-2]
#   y  x z
#1: a  3 2
#2: a  2 2
#3: b  8 1
#4: c 11 3
#5: c 10 3
#6: c  9 3