Desktop Survival Guide
by Graham Williams
A number of operators are available to extract data from matrices.
The single open square bracket [ is used to one or more
elements from a matrix, while the double open square bracket returns
just the specific element specified, requiring all relevant subscripts
to be supplied.
> ds[1:20,] # Rows 1 to 20. > ds[,5:10] # Columns 5 to 10. > ds[,c(3,5,8,9)] # Columns 3, 5, 8, and 9. > lst[] # First element of list lst.
The [ operator can select multiple elements from an object
whilst [[ and
$ select just a single element.