Getting the range of a data frame including zero - r

Question

Here is a simple question. I have a data frame with values ranging from 0 to 3 and I want to get the number of elements of the dataset, which should be 4 in this case. Here is an example of the data:
structure(list(X1 = c(2L, 2L, 2L, 2L, 2L, 1L, 3L, 2L, 2L), X2 = c(1L,
1L, 1L, 2L, 1L, 0L, 2L, 3L, 1L), X3 = c(2L, 1L, 2L, 2L, 0L, 0L,
2L, 3L, 1L), X4 = c(1L, 2L, 2L, 2L, 1L, 2L, 0L, 2L, 2L), X5 = c(1L,
2L, 1L, 2L, 1L, 0L, 1L, 2L, 1L), X6 = c(1L, 2L, 1L, 1L, 1L, 2L,
1L, 2L, 1L)), .Names = c("X1", "X2", "X3", "X4", "X5", "X6"), class = "data.frame", row.names = c(NA,
-9L))
I've tried diff(range(d)) but it doesn't count 0. Thanks in advance.

Answer 1

length(unique(...)) does some possibly unexpected (although thoroughly documented) things when applied to a matrix or data frame.
s <- structure(list(X1 = c(2L, 2L, 2L, 2L, 2L, 1L, 3L, 2L, 2L), X2 = c(1L,
1L, 1L, 2L, 1L, 0L, 2L, 3L, 1L), X3 = c(2L, 1L, 2L, 2L, 0L, 0L,
2L, 3L, 1L), X4 = c(1L, 2L, 2L, 2L, 1L, 2L, 0L, 2L, 2L), X5 = c(1L,
2L, 1L, 2L, 1L, 0L, 1L, 2L, 1L), X6 = c(1L, 2L, 1L, 1L, 1L, 2L,
1L, 2L, 1L)), .Names = c("X1", "X2", "X3", "X4", "X5", "X6"), class = "data.frame", row.names = c(NA,
-9L))
When applied to a data frame, unique returns the unique rows in the data frame. length() then counts the number of columns in the data frame. So in general (I can't think of a counterexample), this will always be equal to ncol(s).
length(unique(s)) ## 6
unique applied to a matrix also returns the unique rows, but now length() counts the total number of elements: for your data this will usually be equivalent to ncol(s)*nrow(s).
length(unique(as.matrix(s))) ## 54
If you want to apply unique to the elements in this situation, you probably want one of the following, all of which collapse the original data frame down to a single vector:
length(unique(as.vector(as.matrix(s)))) ## 4
length(unique(unlist(s))) ## 4
length(unique(c(as.matrix(s)))) ## 4
Whether you want diff(range(x))+1 or length(unique(...)) depends on how you would want to count a data frame composed (for example) entirely of {0,1,2,4} -- should that return 4 or 5? (As #Brian Diggs points out in his answer, diff(range(...))+1 will work on a matrix, without needing to flatten the structure further -- it will also work on an unlist()ed data frame.)

Answer 2

diff(range(d)) returns the difference between minimum and maximum, being 0 and 3 respectively
What you want to do is count how many elements there are in a set. Try length(d)
d <- 0:3
length(d)
Including the comments to this answer... Let the code speak
Example data:
dataset = 1:136
dataset = dataset %% 4
dim(dataset) <- c(4,34) //Now we have a table
diff(range(dataset))+1
It returns 4 like you wanted

Answer 3

Given the structure of d you have now provided, you can do a column-by-column calculation of this.
> diff(range(d$X1))+1
[1] 3
> diff(range(d$X1))+1
[1] 3
> diff(range(d$X2))+1
[1] 4
> diff(range(d$X3))+1
[1] 4
> diff(range(d$X4))+1
[1] 3
> diff(range(d$X5))+1
[1] 3
> diff(range(d$X6))+1
[1] 2
Or you can loop over all the columns
> lapply(d, function(dp) {diff(range(dp))+1})
$X1
[1] 3
$X2
[1] 4
$X3
[1] 4
$X4
[1] 3
$X5
[1] 3
$X6
[1] 2
Or if you want the range for all the columns collectively, treat it as a matrix:
> diff(range(as.matrix(d)))+1
[1] 4