Connect mean points of error bars

Question

In ggplot2 I\'m attempting a simple thing that I just can\'t get for some reason. I have adjusted means and SE in a data frame and want to plot the means, error bars and th

Answer 1

As an alternative to mnel's answer, you could create a new variable, so that you have a column where all 3 groups have the same value:

 data1$all <- "All"

And then use that as the group aesthetic for your line:

ggplot(data1, aes(x=group, y=estimate)) + 
    geom_errorbar(aes(ymin=estimate-SE, ymax=estimate+SE), 
        colour="black", width=.1, position=pd) +
    geom_line(aes(x=group, y=estimate, group=all)) + 
    geom_point(position=pd, size=4)

Mnel's answer is probably more elegant, but this might work better if the groups aren't numbers and can't be converted to numeric so straightforwardly.

Answer 2

If you remove the grouping by group within the ggplot call and set x = as.numeric(group ) within the call to geom_line, the it works.

Also, you don't need to re-reference data1 within geom_line

ggplot(data1, aes(x=group, y=estimate)) + 
  geom_errorbar(aes(ymin=estimate-SE, ymax=estimate+SE), 
  colour="black", width=.1, position=pd) +
  geom_line( aes(x=as.numeric(group), y=estimate)) + 
  geom_point(position=pd, size=4)

If you group by group, then you only have one value for geom_line to create a line from, hence the error message. The same error occurs if ggplot is considering the x or y mapping variables as a factor - this is because if you code a variable as a factor R (and ggplot) will consider them independent groups, and not connect the points - this is sensible default behaiviour.

EDIT - with alphabetic factor labels

This will work with alphabetic factor labels due to the way factors are coded internally by R (ie as.numeric(factor) returns numbers not the factor labels)

ie.e

Changing group to a, b, c

levels(data1[['group']]) <- letters[1:3] 
ggplot(data1, aes(x=group, y=estimate)) + 
  geom_errorbar(aes(ymin=estimate-SE, ymax=estimate+SE), 
  colour="black", width=.1, position=pd) +
  geom_line( aes(x=as.numeric(group), y=estimate)) + 
  geom_point(position=pd, size=4)

Answer 3

You might also look at the 2nd answer to this SO Question If you are working toward a fuller implementation this might save you some time.