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geom_smooth on a subset of data

Here is some data and a plot:

set.seed(18)
data = data.frame(y=c(rep(0:1,3),rnorm(18,mean=0.5,sd=0.1)),colour=rep(1:2,12),x=rep(1:4,each=6))

ggplot(data,aes(x=x,y=y,colour=factor(colour)))+geom_point()+ geom_smooth(method='lm',formula=y~x,se=F)

enter image description here

As you can see the linear regression is highly influenced by the values where x=1. Can I get linear regressions calculated for x >= 2 but display the values for x=1 (y equals either 0 or 1). The resulting graph would be exactly the same except for the linear regressions. They would not "suffer" from the influence of the values on abscisse = 1

like image 594
Remi.b Avatar asked Jun 19 '13 15:06

Remi.b


1 Answers

It's as simple as geom_smooth(data=subset(data, x >= 2), ...). It's not important if this plot is just for yourself, but realize that something like this would be misleading to others if you don't include a mention of how the regression was performed. I'd recommend changing transparency of the points excluded.

ggplot(data,aes(x=x,y=y,colour=factor(colour)))+
geom_point(data=subset(data, x >= 2)) + geom_point(data=subset(data, x < 2), alpha=.2) +
geom_smooth(data=subset(data, x >= 2), method='lm',formula=y~x,se=F)

enter image description here

like image 170
Matthew Plourde Avatar answered Sep 22 '22 19:09

Matthew Plourde