| stepfun | R Documentation |
Given the vectors (x[1], …, x[n]) and
(y[0], y[1], …, y[n]) (one value
more!), stepfun(x, y, ...) returns an interpolating
‘step’ function, say fn. I.e., fn(t) =
c[i] (constant) for t in (
x[i], x[i+1]) and at the abscissa values, if (by default)
right = FALSE, fn(x[i]) = y[i] and for
right = TRUE, fn(x[i]) = y[i-1], for
i=1, …, n.
The value of the constant c[i] above depends on the
‘continuity’ parameter f.
For the default, right = FALSE, f = 0,
fn is a cadlag function, i.e., continuous from the right,
limits from the left, so that the function is piecewise constant on
intervals that include their left endpoint.
In general, c[i] is interpolated in between the
neighbouring y values,
c[i] = (1-f)*y[i] + f*y[i+1].
Therefore, for non-0 values of f, fn may no longer be a proper
step function, since it can be discontinuous from both sides, unless
right = TRUE, f = 1 which is left-continuous (i.e., constant
pieces contain their right endpoint).
stepfun(x, y, f = as.numeric(right), ties = "ordered",
right = FALSE)
is.stepfun(x)
knots(Fn, ...)
as.stepfun(x, ...)
## S3 method for class 'stepfun'
print(x, digits = getOption("digits") - 2, ...)
## S3 method for class 'stepfun'
summary(object, ...)
x |
numeric vector giving the knots or jump locations of the step
function for |
y |
numeric vector one longer than |
f |
a number between 0 and 1, indicating how interpolation outside
the given x values should happen. See |
ties |
Handling of tied |
right |
logical, indicating if the intervals should be closed on the right (and open on the left) or vice versa. |
Fn, object |
an R object inheriting from |
digits |
number of significant digits to use, see |
... |
potentially further arguments (required by the generic). |
A function of class "stepfun", say fn.
There are methods available for summarizing ("summary(.)"),
representing ("print(.)") and plotting ("plot(.)", see
plot.stepfun) "stepfun" objects.
The environment of fn contains all the
information needed;
"x","y" |
the original arguments |
"n" |
number of knots (x values) |
"f" |
continuity parameter |
"yleft", "yright" |
the function values outside the knots |
"method" |
(always |
The knots are also available via knots(fn).
The objects of class "stepfun" are not intended to be used for
permanent storage and may change structure between versions of R (and
did at R 3.0.0). They can usually be re-created by
eval(attr(old_obj, "call"), environment(old_obj))
since the data used is stored as part of the object's environment.
Martin Maechler, maechler@stat.math.ethz.ch with some basic code from Thomas Lumley.
ecdf for empirical distribution functions as
special step functions and plot.stepfun for plotting
step functions.
approxfun and splinefun.
y0 <- c(1., 2., 4., 3.)
sfun0 <- stepfun(1:3, y0, f = 0)
sfun.2 <- stepfun(1:3, y0, f = 0.2)
sfun1 <- stepfun(1:3, y0, f = 1)
sfun1c <- stepfun(1:3, y0, right = TRUE) # hence f=1
sfun0
summary(sfun0)
summary(sfun.2)
## look at the internal structure:
unclass(sfun0)
ls(envir = environment(sfun0))
x0 <- seq(0.5, 3.5, by = 0.25)
rbind(x = x0, f.f0 = sfun0(x0), f.f02 = sfun.2(x0),
f.f1 = sfun1(x0), f.f1c = sfun1c(x0))
## Identities :
stopifnot(identical(y0[-1], sfun0 (1:3)), # right = FALSE
identical(y0[-4], sfun1c(1:3))) # right = TRUE
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