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rggplot2line-ploterrorbar

Change size of a line plot, understand how the size argument works

I'm making a multiple lines plot with errorbars. If I don't use the size argument, everything is fine:

# sample data
Response=runif(4)
ResponseMin=Response-Response/5
ResponseMax=Response+Response/5 
Cases=rep(c("Case1","Case2"),each=2)    
df=data.frame(x=1:2,Average=Response,Lower=ResponseMin,Upper=ResponseMax,Case=Cases)
# let's plot
library(ggplot2)
ggplot(df,aes(x=x,y=Average,colour=Case)) +
geom_line(aes(group=Case)) + 
geom_point() +
geom_errorbar(aes(ymin=Lower,ymax=Upper,width=0.25)) +
labs(y="foo",title="Some plot fu")

enter image description here

However, when I modify the line size, I start getting weird stuff:

ggplot(df,aes(x=x,y=Average,colour=Case)) +
geom_line(aes(group=Case, size = 1)) + 
geom_point() +
geom_errorbar(aes(ymin=Lower,ymax=Upper,width=0.25)) +
labs(y="foo",title="Some plot fu")

enter image description here

Why the extra legend entry "1"? And when I add a size argument for the errobars, it looks like the size of the lines stays the same, whatever the value of size is:

ggplot(df,aes(x=x,y=Average,colour=Case)) +
geom_line(aes(group=Case, size = 1)) + 
geom_point() +
geom_errorbar(aes(ymin=Lower,ymax=Upper,width=0.25, size = 1)) +
labs(y="foo",title="Some plot fu")

enter image description here

ggplot(df,aes(x=x,y=Average,colour=Case)) +
geom_line(aes(group=Case, size = 2)) + 
geom_point() +
geom_errorbar(aes(ymin=Lower,ymax=Upper,width=0.25, size = 2)) +
labs(y="foo",title="Some plot fu")

enter image description here

Can you help me figure out what's happening here?

Solution

  • If you set size inside aes you are mapping it to a variable 

    `1` = 1

    and ggplot2 creates a legend. If you just want to set the size, you can do that outside of aes:

    geom_line(aes(group=Case), size = 1)