tvar {mra} | R Documentation |
Expands a vector of time-varying values into a 2-d matrix of the appropriate size for use in MRA model formulas.
tvar(x, nan=attr(x,"nan"), drop.levels=1)
x |
The vector of time varying values to expand. This can be
a factor (see as.factor ). It is assumed that length(x) =
number of sampling occasions. If not, an error will occur in whatever routine
called this function (e.g., F.3d.model.matrix ). |
nan |
Number of individuals. Default is to use the 'nan' attribute
of x . If nan is not specifed or is not an attribute of x ,
an error is thrown. |
drop.levels |
A vector of integers specifying which levels of a factor
to drop. Only applicable if x is a factor. By default, the
first level of all factors is dropped. drop.levels=length(levels(x))
does the SAS thing and drops the last level of a factor. Specifying a vector
will drop all levels in the vector. E.g., drop.levels=c(1,2,7) drops
the 1st, 2nd, and 7th levels of the factor, whatever they are. First level
of a factor is first element of levels(x) . Second level
of a factor is second element of levels(x) , and so on. Setting
drop.levels to 0, a negative number, or a number greater than the number
of levels will not drop any levels (this is so-called cell mean coding). |
A 2-d matrix of size nan
x length(x)
suitable for passing to the
Fortran DLL of MRA for estimation. Values within columns are contant, values
across columns vary according to x
. If x
is a factor, this matrix
contains 0-1 indicator functions necessary to fit the factor.
If x
is a factor, attributes of the returned matrix are
"levels" = levels of the factor and "contr" = contrasts used in the coding (always
contr.treatment
). For other contrast coding of factors, make your own
2-d matrix with a call to the appropriate function (like contr.poly
).
Trent McDonald, WEST-INC, tmcdonald@west-inc.com
nan <- 30 ns <- 5 time.occ <- as.factor(paste("T",1:ns, sep="")) attr(time.occ,"nan") <- nan time.mat <- tvar(time.occ, drop=ns) # Last occasion is the reference, the SAS and MARK default. dim(time.mat) <- c(nan,ns,length(levels(time.occ))-1) print(time.mat) # each page is the 2-d matrix used in the fit. print(time.mat[1,,]) # compare the above to tvar( 1:ns, nan )