rcspline.restate {Hmisc} | R Documentation |
This function re-states a restricted cubic spline function in the un-linearly-restricted form. Coefficients for that form are returned, along with an S functional representation of this function and a LaTeX character representation of the function.
rcspline.restate(knots, coef, type=c("ordinary","integral"), x="X", lx=nchar(x), norm=2, columns=65, before="& &", after="\", begin="", nbegin=0, digits=max(8, .Options$digits))
knots |
vector of knots used in the regression fit |
coef |
vector of coefficients from the fit. If the length of coef is
k-1 , where k=length(knots) , the first coefficient must be
for the linear term and remaining k-2 coefficients
must be for the constructed terms (e.g., from rcspline.eval ).
If the length of coef is k , an intercept is assumed to be in
the first element.
|
type |
The default is to represent the cubic spline function corresponding
to the coefficients and knots. Set type="integral" to instead represent
its anti-derivative.
|
x |
a character string to use as the variable name in the LaTeX expression for the formula. |
lx |
length of x to count with respect to columns . Default is length
of character string contained by x . You may want to set lx
smaller than this if it includes non-printable LaTeX commands.
|
norm |
normalization that was used in deriving the original nonlinear terms
used in the fit. See rcspline.eval for definitions.
|
columns |
maximum number of symbols in the LaTeX expression to allow before inserting a newline (\\) command. Set to a very large number to keep text all on one line. |
before |
text to place before each line of LaTeX output. Use "& &" for an equation
array environment in LaTeX where you want to have a left-hand prefix
e.g. f(X) & = & or using \lefteqn .
|
after |
text to place at the end of each line of output. |
begin |
text with which to start the first line of output. Useful when adding LaTeX output to part of an existing formula |
nbegin |
number of columns of printable text in begin
|
digits |
number of significant digits to write for coefficients and knots |
a vector of coefficients. The coefficients are un-normalized
and two coefficients are added that are linearly dependent on the
other coefficients and knots. The vector of coefficients has four
attributes. knots
is a vector of knots, latex
is a vector of text strings
with the LaTeX representation of the formula.
columns.used
is the number of columns used in the output string
since the last newline command. function
is an S function, which is
also return in character string format as the text
attribute.
Frank Harrell
Department of Biostatistics, Vanderbilt University
f.harrell@vanderbilt.edu
rcspline.eval
, ns
, rcs
, latex
, Function.transcan
set.seed(1) x <- 1:100 y <- x + rnorm(100, 0, 5) xx <- rcspline.eval(x, inclx=TRUE, nk=4) knots <- attr(xx, "knots") coef <- lsfit(xx, y)$coef options(digits=4) # rcspline.restate must ignore intercept w <- rcspline.restate(knots, coef[-1], x="{\\rm BP}") # could also have used coef instead of coef[-1], to include intercept cat(attr(w,"latex"), sep="\n") xtrans <- eval(attr(w, "function")) # This is an S function of a single argument plot(x, xtrans(x), type="l") # Plots fitted transformation #x <- blood.pressure xx.simple <- cbind(x, pmax(x-knots[1],0)^3, pmax(x-knots[2],0)^3, pmax(x-knots[3],0)^3, pmax(x-knots[4],0)^3) pred.value <- coef[1] + xx.simple %*% w plot(x, pred.value, type='l') # same as above