Question

Probably about 20 chars’ solution. I want colnames to matrix(...) -object or alternative way to create 6×100 dataframe with zeros and colnames:

matrix(rep(0,600),ncol=6)->M

where to access things with title-ids likecol$id and now to access 97th element in col a1 in the matrix, I want to do M$a1[97]. How?

Errr

> matrix(rep(0,600),ncol=6,nrow=100, colnames=c('q1','q2','a1','a2','s1','s2'))
Error in matrix(rep(0, 600), ncol = 6, nrow = 12, colnames = c("q1", "q2",  : 
  unused argument(s) (colnames = c("q1", "q2", "a1", "a2", "s1", "s2"))

Answer 1

1) Use the dimnames parameter in matrix to define column names when creating the matrix. dimnames should be a list of 2 or NULL.

M <- matrix(rep(0,600), ncol = 6, 
            dimnames = list(NULL, c('q1','q2','a1','a2','s1','s2')))

From the help page:

dimnames    
A dimnames attribute for the matrix: NULL or a list of length 2 giving the row and column
names respectively. An empty list is treated as NULL, and a list of length one as row
names. The list can be named, and the list names will be used as names for the dimensions.

Or set the colnames after the fact:

colnames(M) <- c('q1','q2','a1','a2','s1','s2')

2) Use the [ indexing operator for matrices:

> M[97, "a1"]
a1 
 0