R help - Mar 2009 - Display Equation on plot

Hello,

I am using the lm to fit a linear model to data, I was wondering if 
there is a way to display the equation on a plot using the extracted lm 
coefficients?  I am using the plot() function to create the plot/.png.

Example:
lm_mod <- lm(data1~data2)

intercept = 48.54
slope = 0.4856

I want to display equation on a plot as y=0.4856x+48.54

Any thoughts or suggestions are appreciated.

Thanks,
Doug

-- 
---------------------------------
Douglas M. Hultstrand, MS
Senior Hydrometeorologist
Metstat, Inc. Windsor, Colorado
voice: 970.686.1253
email: dmhultst at metstat.com
web: http://www.metstat.com

Douglas M. Hultstrand wrote:
> Hello,
> 
> I am using the lm to fit a linear model to data, I was wondering if 
> there is a way to display the equation on a plot using the extracted lm 
> coefficients?  I am using the plot() function to create the plot/.png.
> 
> Example:
> lm_mod <- lm(data1~data2)
> 
> intercept = 48.54
> slope = 0.4856
> 
> I want to display equation on a plot as y=0.4856x+48.54
> 
> Any thoughts or suggestions are appreciated.

See ?abline:
abline(lm_mod)

Uwe Ligges



> Thanks,
> Doug
>

On 3/24/2009 12:50 PM, Douglas M. Hultstrand wrote:
> Hello,
> 
> I am using the lm to fit a linear model to data, I was wondering if 
> there is a way to display the equation on a plot using the extracted lm 
> coefficients?  I am using the plot() function to create the plot/.png.
> 
> Example:
> lm_mod <- lm(data1~data2)
> 
> intercept = 48.54
> slope = 0.4856
> 
> I want to display equation on a plot as y=0.4856x+48.54
mtext(bquote( y == .(slope) * x + .(intercept)), side=1, line=4)

will put it in the bottom margin.  Use text() with appropriate 
coordinates to put it in the plot area instead.

Duncan Murdoch
> 
> Any thoughts or suggestions are appreciated.
> 
> Thanks,
> Doug
>

Douglas M. Hultstrand <dmhultst <at> metstat.com> writes:
> 
> Hello,
> 
> I am using the lm to fit a linear model to data, I was wondering if 
> there is a way to display the equation on a plot using the extracted lm 
> coefficients?  I am using the plot() function to create the plot/.png.
> 
> Example:
> lm_mod <- lm(data1~data2)
> 
> intercept = 48.54
> slope = 0.4856
> 
> I want to display equation on a plot as y=0.4856x+48.54
see ?bquote for building the equation expression
and ?mtext to display text within margins

e.g.
# generate random x and y values
x <- rnorm(100)
y <- 3*x+15 + rnorm(x)

lm_mod <- lm(y ~ x)

plot(x, y)
abline(lm_mod) # add regression line to the plot

lm_coef <- round(coef(lm_mod), 3) # extract coefficients
mtext(bquote(y == .(lm_coef[2])*x + .(lm_coef[1])), 
adj=1, padj=0) # display equation

regards, 

Matthieu