R: Scatter Plot Smoothing

lowess {base} | R Documentation

## 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, y, f=2/3, iter=3, delta=.01*diff(range(x)))

### Arguments

`x, y` | vectors giving the coordinates of the points in the scatter plot. Alternatively a single plotting structure can be specified.
`f` | 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`.

### 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.

### See Also

`loess` (in package `modreg`), a newer formula based version of `lowess` (with different defaults!).

### Examples

    data(cars)
    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)

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