Filter rows within data.table group if max group value > some value

Question

I am trying to filter all rows within a group in a data.table if a max value within that group is > some value. Below is how I would do it in DPLY and how I got it working in two steps in data.table.

#DPLYR 
df<-data.table(
  x =1:12
  ,y = 1:3
)

df %>% group_by(y) %>% 
  filter(max(x) < 11)

##data.table
df[,max_value :=max(x),by=y][max_value<11]

The output should be

    x y
1:  1 1 
2:  4 1 
3:  7 1 
4: 10 1

Is there a way to do this in one step without creating the column in my dataset? All that I have been able to find are subsetting a group to get one specific value within a group, not return all row of the group that meet the condition.

Answer 1

We can use .I to get the row index, extract the index column and subset

df[df[, .I[max(x) < 11], y]$V1]
#    x y
#1:  1 1
#2:  4 1
#3:  7 1
#4: 10 1

Or another option is .SD

df[, .SD[max(x) < 11], y]