Question

I’m using the strucchange package in order to determine where my curve model segments.

My code looks like this:

l.fit <- loess(data$y~data$x)
px <- predict(l.fit,newdata=data$x)
bp <- breakpoints(px~1)

Now, the output of bp:

Optimal 6-segment partition: 

Call:
breakpoints.formula(formula = px ~ 1)

Breakpoints at observation number:
161 254 347 440 533 

Corresponding to breakdates:
0.2571885 0.4057508 0.5543131 0.7028754 0.8514377 

The breakdates are kind of useless, as my x scale goes from 1 to 700 or so. But the breakpoints themselves are exactly what I want, specifically the last one, 533.

If i type:

bp[1]

I get:

$breakpoints
[1] 161 254 347 440 533

but if I try to assign bp[1] to a new vector, I get nothing. Is there anyway I can isolate the last breakpoint, i.e. 533, and assign it to a variable so I can plot a vertical line at the breakpoint? I need to do this for a couple hundred datasets, so being able to isolate the breakpoints would be really useful.

Thanks!

Answer 1

[ extraction doesn’t drop to the simpliest form, so it remains a list. Use [[ or $ extraction instead to get a numeric vector.

bps <- bp[[1]]

or

bps <- bp$breakpoints

To get the last one, you would need to either count its length and select the last one, or reverse it and select the first:

bps[length(bps)]

or

rev(bps)[1]