[SOLVED] Aggregate of a table along with Total at the bottom; using data.table package

Aggregate of a table along with Total at the bottom; using data.table package

This is a sample data.

library(data.table);
DTmtcars<-as.data.table(mtcars,keep.rownames = TRUE);

I need this summary table, however I also need a total row.

DTmtcars[, .(
QSEC = mean(qsec) ,
DISP = sum(disp)/.N ,
VS =  sum(vs !=0)),  
by = gear]

total row should have these values:

DTmtcars[, .(
QSEC = mean(qsec) ,
DISP = sum(disp)/.N ,
VS =  sum(vs !=0))]

Solution

cube(DTmtcars,
     .(QSEC = mean(qsec) ,
     DISP = sum(disp)/.N ,
     VS =  sum(vs !=0)),  
by = "gear")

Output

    gear     QSEC     DISP    VS
   <num>    <num>    <num> <int>
1:     4 18.96500 123.0167    10
2:     3 17.69200 326.3000     3
3:     5 15.64000 202.4800     1
4:    NA 17.84875 230.7219    14

required output:

> DTmtcars[, .(
+   QSEC = mean(qsec) ,
+   DISP = sum(disp)/.N ,
+   VS =  sum(vs !=0))]
       QSEC     DISP    VS
      <num>    <num> <int>
1: 17.84875 230.7219    14