CODEWITHSUNDEEP
rggplot2plotgraphics
Edgar Santos
Edgar Santos

Reputation: 3514

ggplot2: how to produce smaller points

I have a large dataset that I am plotting using a scatter plot. These points have a unique combination of x,y and therefore they don't overlap, but some of them are very close to each other therefore I'm plotitng them with small size.

1- How to produce smaller point symbols (smaller size) so that the areas are proportional. In this example, the last point does not have an area proportional to the size. I was expecting it 10 smaller than the middle one e.g.:

df <- data.frame(c1 = 1:3, c2 = c(1,1,1))
ggplot(df) + geom_point(aes(x= c1, y = c2), size = c(1, 0.1, 0.01))

2- How does the size in ggplot2 matches the R graphics cex argument e.g.: plot(df$c2 ~ df$c1, cex = c(1, 0.1, 0.01)). Thanks

Upvotes: 4

Views: 11404

Answers (4)

Gustavo
Gustavo

Reputation: 31

Aparently you can get to zero minimum dot sizes, by changing the parameter "stroke" to stoke = 0. Found this solution at this blog post. Works perfect for me!

Upvotes: 0

LuleSa
LuleSa

Reputation: 145

The issue here might be that a point in ggplot consists of an interior and a border part (for lack of better wording). The interior is controlled with fill, alpha, and size, and the border with color and stroke. With size, you will, therefore, only change the size of the interior, while the line thickness of the border will remain unchanged. Try setting stroke = 0and see how that changes your point size in case of smaller values.

Upvotes: 1

neilfws
neilfws

Reputation: 33782

There is a size = argument to geom_point, but you either specify a size for all points:

+ geom_point(size = 0.5)

Or you map the size to one of the columns in your data using aes:

+ geom_point(aes(size = c2))

In the latter case, you can control the range of sizes using scale_size_continuous. The default is min = 1, max = 6. To get e.g. min = 2, max = 8:

+ geom_point(aes(size = c2)) + scale_size_continuous(range = c(2, 8))
  • Note that the "ggplot2 way" is to map data to geoms, not to assign values to each observation
  • and no, size here is different to cex

Upvotes: 10

Justin In Oz
Justin In Oz

Reputation: 310

You can try 

geom_point(shape = ".")

this will make the point 1 pixel in size.

This is from page 70 of ggplot2 second edition by H Wickham

Upvotes: 12

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