Conditional text formatting with ggplot

Question

I've had a good look around this site and others on how to set the hjust and vjust according to a value in a particular column. The following shows how the data is structured (but is a simplified subset of many entries for many years):

    YearStart <- c(2001,2002,2003,2001,2002,2003)
    Team <- c("MU","MU","MU","MC","MC","MC")
    Attendance <- c(67586,67601,67640,33058,34564,46834)
    Position <- c(3,1,3,1,9,16)
    offset <-c()

    df <- data.frame(YearStart,Team,Attendance,Position)

so

> head(df)
  YearStart Team Attendance Position
1      2001   MU      67586        3
2      2002   MU      67601        1
3      2003   MU      67640        3
4      2001   MC      33058        1
5      2002   MC      34564        9
6      2003   MC      46834       16

what I would like to acheive is a vjust value based on the Team. In the following, MU would be vjust=1 and MC would be vjust=-1 so I can control where the data label is located from the data group with which it is associated.

I've tried to hack around a couple of examples that use a function containing a lookup table (it's not a straight ifelse as I have many values for Team) but I can't seem to pass a string to the function through the aes method along these lines:

lut <- list(MU=1,MC=-1)
vj <-function(x){lut[[x]]}
p=ggplot(df, aes(YearStart, Attendance, label=Position, group=Team))+
   geom_point()+
   geom_text(aes(vjust = vj(Team) ) )
print(p)

The following is pseudo(ish)code which applies the labels twice to each group in each location above and below the points.

p=ggplot(df, aes(YearStart, Attendance, label=Position, group=Team))+
   geom_point()+
   geom_text(aes(Team="MU"), vjust=1)+
   geom_text(aes(Team="MC"), vjust=-1)
print(p)

I've tried several other strategies for this and I can't tell whether I'm trying this from the wrong direction or I'm just missing a very trivial piece of ggplot syntax. I've accomplished a stop-gap solution by labelling them manually in Excel but that's not sustainable :-)

Please don't edit your question to refer to answers. This gets very confusing. If you wish to clarify certain points, then by all means do that. If you wish to comment on an answer, then the appropriate place is in the comments following the answer. — Andrie
I have reverted the question, since this is more clear. However, prior to doing that, I noticed an error in your new code. Remember that R is case sensitive, and you used Offset in your data.frame but offset in the ggplot call. — Andrie

Andrie Andrie · Accepted Answer · 2011-11-15T13:30:25

To specify an aesthetic, that aesthetic should be a column in your data.frame.

(Notice also that your lookup function should have single brackets, not double.)

And a final thought: vjust and hjust are strictly only defined between [0, 1] for left/bottom and right/top justification. In practise, however, it is usually possible to extend this. I find that settings of (-0.2, 1.2) work quite well, in most cases.

lut <- list(MU=-0.2, MC=1.2)
vj <- function(x) lut[x]

df$offset <- vj(df$Team)

library(ggplot2)
ggplot(df, aes(YearStart, Attendance, label=Position, group=Team)) +
    geom_point(aes(colour=Team)) +
    geom_text(aes(vjust = offset))

enter image description here

Conditional text formatting with ggplot

1 Answers