lowess: Scatter Plot Smoothing

Description

This function performs the computations for the LOWESS smoother (see the reference below). lowess returns a list containing components x and y which give the coordinates of the smooth. The smooth should be added to a plot of the original points with the function lines.

Usage

lowess(x, ...)
## S3 method for class 'default':
lowess(x, y = NULL, f = 2/3, iter = 3, delta = 0.01 *
                  diff(range(xy$x[o])), ...)
## S3 method for class 'formula':
lowess(formula,data = parent.frame(), subset, na.action, 
               f=2/3,  iter=3, delta=.01*diff(range(mf[-response])), ... )

Arguments

formula

formula providing a single dependent variable (y) and an single independent variable (x) to use as coordinates in the scatter plot.

data

a data.frame (or list) from which the variables in `formula' should be taken.

subset

an optional vector specifying a subset of observations to be used in the fitting process.

x, y

vectors giving the coordinates of the points in the scatter plot. Alternatively a single plotting structure can be specified.

the smoother span. This gives the proportion of points in the plot which influence the smooth at each value. Larger values give more smoothness.

iter

the number of robustifying iterations which should be performed. Using smaller values of iter will make lowess run faster.

delta

values of x which lie within delta of each other replaced by a single value in the output from lowess.

na.action

a function which indicates what should happen when the data contain `NA's. The default is set by the `na.action' setting of `options', and is `na.fail' if that is unset. The ``factory-fresh'' default is `na.omit'.

...

parameters for methods.

References

Cleveland, W. S. (1979) Robust locally weighted regression and smoothing scatterplots. J. Amer. Statist. Assoc. 74, 829--836.

Cleveland, W. S. (1981) LOWESS: A program for smoothing scatterplots by robust locally weighted regression. The American Statistician, 35, 54.

Examples

Run this code

data(cars)

# default method
plot(cars, main = "lowess(cars)")
lines(lowess(cars), col = 2)
lines(lowess(cars, f=.2), col = 3)
legend(5, 120, c(paste("f = ", c("2/3", ".2"))), lty = 1, col = 2:3)

# formula method
plot(dist ~ speed, data=cars, main = "lowess(cars)")
lines(lowess(dist ~ speed, data=cars), col = 2)
lines(lowess(dist ~ speed, data=cars, f=.2), col = 3)
legend(5, 120, c(paste("f = ", c("2/3", ".2"))), lty = 1, col = 2:3)

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