ggplot error using linetype and group aesthetics

Question

I'm trying to make plot based on the following data

dt <- data.frame(ValuationDate = seq.Date(as.Date("2014-1-1"), 
                 as.Date("2014-7-1"), by = "month"), 
                 Adjuster = factor(c("Bob","Bob","Sue","Sue","Sue","Sue","Bob")),
                 Paid = c(1,2,3,4,5,6,7), Incurred = c(3,5,9,9,10,8,7))
dt <- melt(dt, measure.vars = c("Paid", "Incurred"), 
           variable.name = "Value", value.name = "Amount")
dt
   ValuationDate Adjuster    Value Amount
1     2014-01-01      Bob     Paid      1
2     2014-02-01      Bob     Paid      2
3     2014-03-01      Sue     Paid      3
4     2014-04-01      Sue     Paid      4
5     2014-05-01      Sue     Paid      5
6     2014-06-01      Sue     Paid      6
7     2014-07-01      Bob     Paid      7
8     2014-01-01      Bob Incurred      3
9     2014-02-01      Bob Incurred      5
10    2014-03-01      Sue Incurred      9
11    2014-04-01      Sue Incurred      9
12    2014-05-01      Sue Incurred     10
13    2014-06-01      Sue Incurred      8
14    2014-07-01      Bob Incurred      7

For each ValuationDate, there is a "Paid" amount and an "Incurred" amount which I'd like to plot over time, associating each time period with an Adjuster. When I try doing

#with grouping variable and linetype (error)
ggplot(data = dt) + geom_step(aes(x = ValuationDate, 
                                  y = Amount, group = Value, 
                                  color = Adjuster, linetype = Value))

I get "Error: geom_path: If you are using dotted or dashed lines, colour, size and linetype must be constant over the line"

However the following two plots work

#with grouping variable, without linetype
ggplot(data = dt) + geom_step(aes(x = ValuationDate, y = Amount,
                                  group = Value, color = Adjuster))

enter image description here

#with linetype, without grouping variable
ggplot(data = dt) + geom_step(aes(x = ValuationDate, y = Amount,
                                  color = Adjuster, linetype = Value))

enter image description here

What gives?

What output are you looking for? How many total lines, representing what? — arvi1000
My output should have two lines, very similar to the first graph I displayed. The issue with that graph though, is that there's no distinction between what is "Paid" and what is "Incurred". — Ben

tonytonov tonytonov · Accepted Answer · 2014-11-19T07:33:12

Let's take a look at the piece of code that generates the error:

# Work out whether we should use lines or segments
attr <- ddply(munched, .(group), function(df) {
  data.frame(
    solid = identical(unique(df$linetype), 1),
    constant = nrow(unique(df[, c("alpha", "colour","size", "linetype")])) == 1
  )
})
solid_lines <- all(attr$solid)
constant <- all(attr$constant)
if (!solid_lines && !constant) {
  stop("geom_path: If you are using dotted or dashed lines",
    ", colour, size and linetype must be constant over the line",
    call.=FALSE)
}

So if there are at least two different linetypes, all other aes should be unique. I cannot say why exactly this limitation is present, probably it caused some rendering related issues.

You can make the lines distinguishable by other means, e.g. by varying size or alpha instead of linetype. Another possibility would be adding

geom_point(aes(x = ValuationDate, y = Amount, group = Value, shape = Value), size = 3)

enter image description here

ggplot error using linetype and group aesthetics

2 Answers