You should use only plain text emails, provide sample data, and indicate any
relevant packages that you had to load. First let's load the necessary package
and create some data:
> library(segmented)
> set.seed(42)
> x <- sort(runif(60, 10, 60))
> int <- c(rep(0, 20), rep(60, 20), rep(-80, 20))
> slp <- c(rep(2, 20), rep(0, 20), rep(3, 20))
> y <- int + slp*x + rnorm(60, 0, 2)
> plot(x, y)
You should have a plot showing 2 break points. Using psi=mean(x) puts a single
breakpoint in the middle of the distribtution so we have to be more specific:
> lin.mod <- lm(y~x)
> segmented.mod <- segmented(lin.mod, seg.Z = ~x, psi= c(25, 55))
> plot(segmented.mod, add=T)
> sl <- slope(segmented.mod)
> inter <- intercept(segmented.mod)
Now your plot shows the segmented model. You need to know what intercept() is
returning so you should look at the manual page: ?intercept. It returns a list
of matrices (one matrix for each independent variable). You have only one, x,
so you get a list with one element.
> str(inter)
List of 1
$ x: num [1:3, 1] -0.179 60.25 -86.77
..- attr(*, "dimnames")=List of 2
.. ..$ : chr [1:3] "intercept1" "intercept2" "intercept3"
.. ..$ : chr "Est."
To get the first matrix without knowing its name and the last row:
> tail(inter[[1]], 1)
Est.
intercept3 -86.77
If you want to strip off the labels:
> as.vector(tail(inter[[1]], 1))
[1] -86.77
-----------------------------
David L. Carlson
Department of Anthropology
Texas A&M University
-----Original Message-----
From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Narendra Modi
Sent: Tuesday, July 5, 2016 1:42 PM
To: R-help@r-project.org
Subject: [R] How to extract "specific"/"last" intercept value from segmented
package.
I am able to perform regression on a dataset as below:
plot(x,y)
lin.mod <- lm(y~x)
m <- mean(x)
m
segmented.mod <- segmented(lin.mod, seg.Z = ~x, psi= m)
plot(segmented.mod, add=T)
sl <- slope(segmented.mod)
inter <- intercept(segmented.mod)
summary(segmented.mod) # Show Summary
sl # show all the slopes
inter # show all the intercepts
In my dataset, the above method correctly identifies the breakpoints and
hence I get two intercepts.
> inter
$x
Est.
intercept1 -3.269
intercept2 -19.980
What I am interested is the "intercept2" value. How can I obtain this?
The method needs to be dynamic as in if the next dataset has 3 intercepts,
I would like to get "intercept3 value.
PD
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
