Question

I would like to produce a scatter plot with ggplot2, which contains both a regression line through all data points (regardless which group they are from), but at the same time varies the shape of the markers by the grouping variable. The code below produces the group markers, but comes up with TWO regression lines, one for each group.

#model=lm(df, ParamY~ParamX)
p1<-ggplot(df,aes(x=ParamX,y=ParamY,shape=group)) + geom_point() + stat_smooth(method=lm)

How can I program that?

Answer 1

you shouldn’t have to redo your full aes in the geom_point and add another layer, just move the shape aes to the geom_point call:

df <- data.frame(x=1:10,y=1:100+5,grouping = c(rep("a",10),rep("b",10)))
ggplot(df,aes(x=x,y=y)) + 
geom_point(aes(shape=grouping)) + 
stat_smooth(method=lm)

EDIT:

To help with your comment:

because annotate can end up, for me anyway, with the same labels on each facet. I like to make a mini data.frame that has my variable for faceting and the facet levels with another column representing the labels I want to use. In this case the label data frame is called dfalbs.

Then use this to label data frame to label the facets individually e.g.

df <- data.frame(x=1:10,y=1:10,grouping =   
                  c(rep("a",5),rep("b",5)),faceting=c(rep(c("oneR2","twoR2"),5)))


dflabs <- data.frame(faceting=c("oneR2","twoR2"),posx=c(7.5,7.5),posy=c(2.5,2.5))

ggplot(df,aes(x=x,y=y,group=faceting)) + 
       geom_point(aes(shape=grouping),size=5) + 
       stat_smooth(method=lm) +
       facet_wrap( ~ faceting) +
       geom_text(data=dflabs,aes(x=posx,y=posy,label=faceting))