R help - Sep 2010 - How to set the limit of abline (regression line of lm)

Dear List,



I ran a regression model using lm and produced a regression line using
abline.


The line ranges from -20 to 20 in x axis,

and the section I only want is from -20 to 0.



Please kindly advise any function in abline () to set the range of x axes.

Thank you



Elaine

	[[alternative HTML version deleted]]

On Mon, 2010-09-20 at 17:31 +0800, elaine kuo wrote:
> Dear List,
> 
> 
> 
> I ran a regression model using lm and produced a regression line using
> abline.
> 
> 
> The line ranges from -20 to 20 in x axis,
> 
> and the section I only want is from -20 to 0.
> 
> 
> 
> Please kindly advise any function in abline () to set the range of x axes.
You can't; these are already set by the plot, and abline only *adds* to
the plot. You need to think about this a different way. What you want
are the model predictions for points spread over the range (-20, 0]. So
set up a new data set of 'x' values and use predict() to generate the
appropriate 'y' values.

Here's an example:

set.seed(123)
dat <- data.frame(x = sample(seq(-20, 20, length = 100)))
dat <- within(dat, y <- 8 + (1.8 * x) + (10 * rnorm(100)))
mod <- lm(y ~ x, data = dat)

## now plot the data
plot(y ~ x, data = dat)

## now predict 50 values spread evenly on range (-20, 0]
newdat <- data.frame(x = seq(-20, 0, length = 50))
newdat <- within(newdat, ypred <- predict(mod, newdat))

## add these predictions as a line to the plot
lines(ypred ~ x, data = newdat, col = "red", lwd = 2)

HTH

G
> Thank you
> 
> 
> 
> Elaine
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
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http://www.R-project.org/posting-guide.html
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On 09/20/2010 07:31 PM, elaine kuo wrote:
> Dear List,
>
>
>
> I ran a regression model using lm and produced a regression line using
> abline.
>
>
> The line ranges from -20 to 20 in x axis,
>
> and the section I only want is from -20 to 0.
>
>
>
> Please kindly advise any function in abline () to set the range of x axes.
>
Hi Elaine,
As already noted, you may not really want to do this, but ablineclip in 
the plotrix package will do it for you.

Jim

Look at the clip function for one approach.  You specify the clipping region,
then do abline and it only shows up in the region specified.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of elaine kuo
> Sent: Monday, September 20, 2010 3:32 AM
> To: r-help at r-project.org
> Subject: [R] How to set the limit of abline (regression line of lm)
> 
> Dear List,
> 
> 
> 
> I ran a regression model using lm and produced a regression line using
> abline.
> 
> 
> The line ranges from -20 to 20 in x axis,
> 
> and the section I only want is from -20 to 0.
> 
> 
> 
> Please kindly advise any function in abline () to set the range of x
> axes.
> 
> Thank you
> 
> 
> 
> Elaine
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.