Description Usage Arguments Value Author(s) Examples
This is designed for adding horizontal lines that show predicted
values to a plot of observed values versus xvalues,
in rpart
regression. Where predicted values change
between two successive xvalues lines are extended to the midway
point. This reflects the way that predict.rpart
handles predictions for new data.
1 
x 
Vector of predictor variable values. 
y 
Vector of predicted values. 
... 
Additional graphics parameters, for passing through to the

Lines are added to the current graph.
John Maindonald
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24  x < c(34, 18, 45, 18, 27, 24, 34, 20, 24, 28, 21, 18)
y < c(14, 11, 12, 9, 4, 11, 6, 9, 4, 10, 9, 2)
hat < c(10.5, 7.75, 10.5, 7.75, 7, 7, 10.5, 7.75, 7, 10.5, 7, 7.75)
plot(x, y)
addhlines(x, hat, lwd=2, col="gray")
## The function is currently defined as
function(x,y, ...){
ordx < order(x)
xo < x[ordx]
yo < y[ordx]
breaks < diff(yo)!=0
xh < c(xo[1],0.5*(xo[c(FALSE,breaks)]+xo[c(breaks, FALSE)]))
yh < yo[c(TRUE, breaks)]
y3 < x3 < numeric(3*length(xh)1)
loc1 < seq(from=1, to=length(x3), by=3)
x3[loc1] < xh
x3[loc1+1]< c(xh[1], max(x))
x3[loc1[length(loc1)]+2] < NA
y3[loc1[length(loc1)]+2] < NA
y3[loc1] < yh
y3[loc1+1] < yh
lines(x3,y3, ...)
}

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