left One-sided left smooth for a Locfit model. left


locfit(y~left(x), ev="data", deg=1)


The left() function is used in a locfit model formula to specify a one-sided smooth: when fitting at a point x, only data points with x_i \le x should be used. This can be useful in estimating points of discontinuity, and in cross-validation for forecasting a time series.

When using this function, it will usually be necessary to specify an evaluation structure, since the fit is not smooth and locfit's interpolation methods are unreliable. Also, it is usually best to use deg=0 or deg=1, otherwise the fits may be too variable. If nearest neighbor bandwidth specification is used, it does not recognize left().


numeric variable.


# compute left and right smooths
xev <- (1945:1988)+0.5
fitl <- locfit(thickness~left(year), alpha=c(0,10), deg=1, ev=xev, data=penny)
fitr <- locfit(thickness~right(year),alpha=c(0,10), deg=1, ev=xev, data=penny)
# plot the squared difference, to show the change points.
plot( xev, (predict(fitr,where="ev") - predict(fitl,where="ev"))^2 )

See Also:

lfbas, locfit, right

Key Words:

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Author: Catherine Loader