interpSpline {splines}R Documentation

Create an Interpolation Spline


Create an interpolation spline, either from x and y vectors, or from a formula/data.frame combination.


interpSpline(obj1, obj2, bSpline = FALSE, period = NULL,
             na.action =


obj1 Either a numeric vector of x values or a formula.
obj2 If obj1 is numeric this should be a numeric vector of the same length. If obj1 is a formula this can be an optional data frame in which to evaluate the names in the formula.
bSpline If TRUE the b-spline representation is returned, otherwise the piecewise polynomial representation is returned. Defaults to FALSE.
period An optional positive numeric value giving a period for a periodic interpolation spline.
na.action a optional function which indicates what should happen when the data contain NAs. The default action (na.omit) is to omit any incomplete observations. The alternative action causes interpSpline to print an error message and terminate if there are any incomplete observations.


An object that inherits from class spline. The object can be in the B-spline representation, in which case it will be of class nbSpline for natural B-spline, or in the piecewise polynomial representation, in which case it will be of class npolySpline.


Douglas Bates and Bill Venables

See Also

splineKnots, splineOrder, periodicSpline.


ispl <- interpSpline( women$height, women$weight )
ispl2 <- interpSpline( weight ~ height,  women )
# ispl and ispl2 should be the same
plot( predict( ispl, seq( 55, 75, len = 51 ) ), type = "l" )
points( women$height, women$weight )
plot( ispl )    # plots over the range of the knots
points( women$height, women$weight )
splineKnots( ispl )

[Package splines version 2.2.1 Index]