omit empty cells in crosstab?

small example:

a<-c(1.1, 2.1, 9.1)
b<-cut(a,0:10)
c<-data.frame(b,b)
d<-table(c)
dim(d) 
##result: c(10, 10)

But only 9 of the 100 cells are non-zero.
If there were 10 columns, the table have 10 dimensions each of length 10, so
have 10^10 elements, too much even to fit in memory

Hi Steve

In your only 3 cells > 0

d

b.1
b        (0,1] (1,2] (2,3] (3,4] (4,5] (5,6] (6,7] (7,8] (8,9] (9,10]
  (0,1]      0     0     0     0     0     0     0     0     0      0
  (1,2]      0     1     0     0     0     0     0     0     0      0
  (2,3]      0     0     1     0     0     0     0     0     0      0
  (3,4]      0     0     0     0     0     0     0     0     0      0
  (4,5]      0     0     0     0     0     0     0     0     0      0
  (5,6]      0     0     0     0     0     0     0     0     0      0
  (6,7]      0     0     0     0     0     0     0     0     0      0
  (7,8]      0     0     0     0     0     0     0     0     0      0
  (8,9]      0     0     0     0     0     0     0     0     0      0
  (9,10]     0     0     0     0     0     0     0     0     0      1

If you desire use simple code to find only cell>0 use this

 table(interaction(c,drop=T))

  (1,2].(1,2]   (2,3].(2,3] (9,10].(9,10] 
            1             1             1

Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
Brazil