ggplot2 density plotting different size of data in R

Question

I have two data sets, their size is 500 and 1000. I want to plot density for these two data sets in one plot.
I have done some search in google.

the data sets in above threads are the same

df <- data.frame(x = rnorm(1000, 0, 1), y = rnorm(1000, 0, 2), z = rnorm(1000, 2, 1.5))

But if I have different data size, I should normalize the data first in order to compare the density between data sets.

Is it possible to make density plot with different data size in ggplot2?

I think density plots scale the data to area = 1 by default, so there is no need to correct for sample size. Someone correct me if I'm wrong. — neilfws
– neilfws, Commented Dec 7, 2017 at 4:32
@neilfws yes, I think these data have scaled. But I don't know they scaled one by one or together — l0o0
– l0o0, Commented Dec 7, 2017 at 4:53

Claus Wilke · Accepted Answer · 2017-12-08 05:18:46Z

10

By default, all densities are scaled to unit area. If you have two datasets with different amounts of data, you can plot them together like so:

df1 <- data.frame(x = rnorm(1000, 0, 2))
df2 <- data.frame(y = rnorm(500, 1, 1))

ggplot() + 
  geom_density(data = df1, aes(x = x), 
               fill = "#E69F00", color = "black", alpha = 0.7) + 
  geom_density(data = df2, aes(x = y),
               fill = "#56B4E9", color = "black", alpha = 0.7)

However, from your latest comment, I take that that's not what you want. Instead, you want the areas under the density curves to be scaled relative to the amount of data in each group. You can do that with the ..count.. aesthetics:

df1 <- data.frame(x = rnorm(1000, 0, 2), label=rep('df1', 1000))
df2 <- data.frame(x = rnorm(500, 1, 1), label=rep('df2', 500))
df=rbind(df1, df2)

ggplot(df, aes(x, y=..count.., fill=label)) + 
  geom_density(color = "black", alpha = 0.7) + 
  scale_fill_manual(values = c("#E69F00", "#56B4E9"))

edited Dec 8, 2017 at 5:18

answered Dec 7, 2017 at 5:14

Claus Wilke

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4 Comments

l0o0 Over a year ago

It looks like two data are scaled to 1, But I want to combine two data first, and then scale the combined data. Is it possible?

Claus Wilke Over a year ago

You'll have to be more precise in describing what it is you want to do. There are many different ways one could "combine" data, and none that I can think of would make sense in this context. Is there anything wrong with the plot I made?

l0o0 Over a year ago

Well, I want to combine two data by

df1 <- data.frame(x = rnorm(1000, 0, 2), label=rep('df1', 1000)); df2 <- data.frame(x = rnorm(500, 1, 1), label=rep('df2', 500)); df=rbind(df1, df2)

. df contains df1 and df2. Now I want to plot density grouped by label. I think the auc of df1 is 2/3 of total, df2 is 1/3

cryptic0 Over a year ago

If no legend is desired, how does one apply colors? Can we do this? fill=c("#E69F00", "#56B4E9") inside geom_density()?

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