ggplot2 - How to define more line types for graphs in R (custom linetype)?

Question

There are 6 line types defined for plots in R defined as "dashed", "longdash" ... Link

How can I define more types if I have more that 6 series to plot ? The graph lines can be distinguished based on colour in the soft copy but is not suitable for black and white printing.

Are there more options available or do I need to define them based on combining lines and points as in the reference link?

plot(x, type = "b", pch = 0, lty = "dotted")

Some google search suggested that patterns of on/off can also be specified with strings of 2, 4, 6, or 8 characters (non-zero hexadecimal characters, 1–9 and a–f) and the pre-set styles are “dashed” = “44", “dotted” = “13”, “dotdash” = “1343”, “longdash” = “73”, “twodash” = “2262”.

But seems it will be a lot of hit and trial to use this to define new line types which will be distinguishable on B&W printing.

Edit :

If points and line styles are combined, how can I define the set of line types in such a way that they can be input as

plot(DF, ..., col = 1:ncol(DF), lty = 1:ncol(DF))
# where DF is the set of data to be plotted. 

Thanks a lot.

Answer 1

As you have mentioned in your link, legal values are the strings "blank", "solid", "dashed", "dotted", "dotdash", "longdash", and "twodash". Alternatively, the numbers 0 to 6 can be used (0 for "blank", 1 for "solid", ...).

Moreover, one can also use strings that define the linetype with up to 8 hexadecimal digits (each digit specifying the length of interleaved lines and gaps).

Here an example , using linetype aes in ggplot2 equivalent to lty in base R. This way you can get more than the 6 predefined types.

library(ggplot2)
d=data.frame(lt=c("blank", "solid", "dashed", "dotted", 
                  "dotdash", "longdash", "twodash", "1F", 
                  "F1", "4C88C488", "12345678"))
ggplot() +
  scale_x_continuous(name="", limits=c(0,1), breaks=NULL) +
  scale_y_discrete(name="linetype") +
  scale_linetype_identity() +
  geom_segment(data=d, mapping=aes(x=0, xend=1, y=lt, yend=lt, linetype=lt))

Explanation:

"1F": dash length 1, gap length F (15)
"F1": dash length F (15), gap length 1
"4C88C488": dash (4), gap (C=12), dash (8), gap (8), dash (C=12), ...
"12345678": dash (1), gap (2), dash (3), gap (4), ...

PS: the solution is adopted from this link.