Request: support providing shapes as names rather than integers

[daattali]

Currently if I want to use ggplot and make the points a certain shape, I need to say "shape=5" for example. Magic numbers like that are inconvenient: the author needs to figure iut what number means what shape, and the person reading the code has no idea what shape that'll be.

It'd be awesome to be able to say "geom_point (shape='diamond')

@thomasp85

[daattali]

Suggestion (I don't have any strong opinion about the naming, just putting this out there so that others can improve on it or implement it):

0: square-open
1: circle-open
2: triangle-up-open
3: cross
4: x-mark (I didn't want to use simply "x" because currently using "x" or any other letter actually uses that letter)
5: diamond-open
6: triangle-down-open
7: square-x
8: asterisk
9: diamond-x
10: circle-cross
11: star
12: square-cross
13: circle-x
14: square-triangle
15: square
16: circle
17: triangle-up
18: diamond
19: circle (I can't figure out the difference between this and 16)
20: circle-small
21: circle-fill
22: square-fill
23: diamond-fill
24: triangle-up-fill
25: triangle-down-fill

[has2k1]

@daattali, If I recall correctly, 16 & 19 can vary in appearance on some OSes depending on the underlying devices. e.g one of them may be aliased and the other not aliased.

[smouksassi]

from the documentation ggplot shapes are like pch base graphics parameter and in the pch help we have:
The difference between pch = 16 and pch = 19 is that the latter uses a border and so is perceptibly larger when lwd is large relative to cex.

[daattali]

Thanks Samer :)

[hturner]

I have a few suggestions for improvements:

• As the names will be specified as character strings, you may as well allow spaces for readability - otherwise perhaps use snake_case for general consistency with ggplot2 conventions.
• Aim for consistency with the naming in ?pch, i.e. describe fill first, use same names for shapes. However, I like your suggestion to have some defaults to avoid long names - as well the default being a solid shape, I suggest assuming triangles are point up unless otherwise stated.
• Use "plus" and "cross" vs "cross" and "x-mark": "plus" is unambiguous, "cross" can imply different shapes, but is often used for an x mark and works better for combinations of shapes.
• If we think of 14 as a square with a chevron on top, we can have the convention that the closed shape always comes first (incidentally the orientation of the triangle comes out differently when I plot it from how it is in ?pch - different OS? different R version? Anyway, chevron works both ways).

Putting all together:

0: open square
1: open circle
2: open triangle
3: plus
4: cross
5: open diamond
6: open triangle down [or point down for consistency with ?pch]
7: square cross
8: asterisk
9: diamond plus
10: circle plus
11: star
12: square plus
13: circle cross
14: square chevron
15: square
16: small circle [as this is the one without the border, smaller than 1 and 19]
17: triangle
18: diamond
19: circle
20: bullet
21: filled circle
22: filled square
23: filled diamond
24: filled triangle
25: filled triangle down [or point down]

[hadley]

This would be a pull request if someone else wanted to implement it. You'd need:

• A function that translated names to numbers (probably using match.arg())
• To call that function in geom_point()

[hturner]

This could be a "good first issue" - now that GitHub is promoting this label to help potential first-time contributors discover issues, it would be good to see this being used in the R community. An accessible ggplot2 issue would be a good way to promote this.

[hadley]

Agreed - I don't have the resources right now to do that systematically, but I will in the near future.

[daniel-barnett]

I've implemented this so far with the strings from @hturner in snake case. Does anybody else have any suggestions/opinions on some of the strings such as "point down" vs simply "down", etc? "filled_triangle_point_down" feels like it's getting a bit lengthy to my eyes, so I've went with "down" for now.

[ptoche]

symbols 21, 22, 23, 24, 25 are special in that they work with both fill and color, whereas the other symbols will ignore fill. Is there a case for making them a more convenient group of symbols to call? e.g. naming them simply "circle", "square", etc. without prefixing with "filled"...

[daniel-barnett]

It depends how we want to treat the relation between the default shape set (which do not fill) and what the strings correspond to.

[daniel-barnett]

To make people's lives easier, here goes the proposed correspondence between strings and shape numbers:

library(ggplot2)

.pch_table <- c("0" =  "open_square",
                "1" =  "open_circle",
                "2" =  "open_triangle",
                "3" =  "plus",
                "4" =  "cross",
                "5" =  "open_diamond",
                "6" =  "open_triangle_down",
                "7" =  "square_cross",
                "8" =  "asterisk",
                "9" =  "diamond_plus",
                "10" = "circle_plus",
                "11" = "star",
                "12" = "square_plus",
                "13" = "circle_cross",
                "14" = "square_triangle",
                "15" = "square",
                "16" = "small_circle",
                "17" = "triangle",
                "18" = "diamond",
                "19" = "circle",
                "20" = "bullet",
                "21" = "filled_circle",
                "22" = "filled_square",
                "23" = "filled_diamond",
                "24" = "filled_triangle",
                "25" = "filled_triangle_down")

df_shapes <- data.frame(shape = 0:25, shape_name = factor(paste0(0:25, " ('", .pch_table, "')")))

ggplot(df_shapes, aes(0, 0, shape = shape)) +
  geom_point(aes(shape = shape), size = 5, fill = 'red', stroke = 2) +
  scale_shape_identity() +
  facet_wrap(~reorder(shape_name, shape)) +
  theme_void()

[ptoche]

Nice. There is room for disagreement about the relative merits of filled_circle and circle_filled or filled.circle or circle.filled. I was under the impression that x_y was more for functions, e.g. geom_boxplot while x.y was more for function arguments, e.g. outlier.shape. I could be wrong. Also there are situations where, say if you import a spreadsheet, a circle filled gets converted to circle.filled so possibly some benefits from having dots. I have no strong opinion. Personally I rarely use shapes outside of 21-26 and have them memorized.