Let x = c(1, 2, 3) be a vector. I use bs function in the splines package of R to generate a matrix of B splines evaluated at x.
require(splines)
x <- c(1, 2, 3)
bs.x <- bs(x, knots = c(1.5, 2.5))
The output bs.x is as follows,
1 2 3 4 5
[1,] 0.00000000 0.0000000 0.0000000 0.00000000 0
[2,] 0.05555556 0.4444444 0.4444444 0.05555556 0
[3,] 0.00000000 0.0000000 0.0000000 0.00000000 1
attr(,"degree")
[1] 3
attr(,"knots")
[1] 1.5 2.5
attr(,"Boundary.knots")
[1] 1 3
attr(,"intercept")
[1] FALSE
attr(,"class")
[1] "bs" "basis" "matrix"
Clearly, besides the basis matrix, bs.x has other attributes. My question is how to get rid of these attributes. I need to do this, because ultimately, I need to run Matrix(bs.x), which throws me the following error message.
Error in as(x, "matrix") :
internal problem in as(): “bs” is(object, "matrix") is
TRUE, but the metadata asserts that the 'is' relation is FALSE
I guess this is because matrix is one of the classes that bs.x belongs to. At this moment, I do the following dumb thing.
bs.x <- matrix(as.numeric(bs.x), nr = nrow(bs.x))
Is there a better alternative? Thanks in advance.
Not a whole lot better, but
attributes(bs.x) <- attributes(bs.x)["dim"]
seems to work. (Reassigns the attributes of bs.x to be only the dim attribute.)