overlaying frequency histograms or density plots in R

Hello,

First of all, I believe you want argument fill, not colour. In ggplot2
colour is about the border and fill about the interior.

As for the question,

1. Create a basic plot with the common aesthetics.


library(ggplot2)

pp_ALL <- iris[c(1, 5)]
names(pp_ALL) <- c("VALUE", "EXP")

p <- ggplot(data = pp_ALL, mapping = aes(x = VALUE, fill = EXP))



2. geom_density should use alpha transparency, since the densities
overlap. colour = NA removes the densities black border.


p + geom_density(alpha = 0.5, colour = NA)


3. y = ..density.. plots relative frequencies histograms, for the
default absolute frequencies or counts, comment the mapping out.

position = position_dodge() allows for extra goodies, such as to change
the space between bars, their width or to keep empty spaces when some
factor levels are missing (preserve = "single").

For the test data, with 50 elements per factor level, use a much smaller
number of bins.

Package scales has functions to display labels in percent format, there
is no need to multiply by 100.


p + geom_histogram(
   mapping = aes(y = ..density..),
   position = position_dodge(),
   bins = 10)

p + geom_histogram(
   mapping = aes(y = ..density..),
   position = position_dodge(),
   bins = 10) +
   scale_y_continuous(labels = scales::label_percent())


Hope this helps,

Rui Barradas


?s 07:43 de 25/02/21, Bogdan Tanasa escreveu:

Thanks a lot Petr !

shall i uses "dodge" also for the RELATIVE FREQUENCY HISTOGRAMS :

p <- ggplot(iris, aes(x=Sepal.Length, y=..count../sum(..count..)*100,
colour=Species))
p+geom_histogram(position="dodge")

or is there any other way to display the RELATIVE FREQUENCY HISTOGRAMS ?

thanks again !

On Wed, Feb 24, 2021 at 11:00 PM PIKAL Petr <petr.pikal at precheza.cz>

wrote:

Hi

You should use position dodge.

p <- ggplot(iris, aes(x=Sepal.Length, colour=Species))
p+geom_density()
p <- ggplot(iris, aes(x=Sepal.Length, y=..density.., colour=Species))
p+geom_histogram(position="dodge")

Cheers
Petr

-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of Bogdan Tanasa
Sent: Wednesday, February 24, 2021 11:07 PM
To: r-help <r-help at r-project.org>
Subject: [R] overlaying frequency histograms or density plots in R

Dear all, we do have a dataframe with a FACTOR called EXP that has 3

LEVELS ;

  head(pp_ALL)
     VALUE  EXP
1 1639742 DMSO
2 1636822 DMSO
3 1634202 DMSO

shall i aim to overlay the relative frequency histograms, or the

density

histograms for the FACTOR LEVELS,

please would you let me know why the following 2 pieces of R code show
very different results :

ggplot(pp_ALL, aes(x=VALUE, colour=EXP)) + geom_density()

versus

ggplot(data=pp_ALL) +
        geom_histogram(mapping=aes(x=VALUE, y=..density.., colour=EXP),
  bins=1000)

thanks,

bogdan

ps : perhaps i shall email to the folks on ggplot2 mailing list too ...

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