R help - Apr 2009 - ggplot2 - boxplot of variables / columns

Hi,

ggplot/qplot is great - it has really helped me do some nice things.
However, simple boxplot of different columns/variables is a bit
tricky, because of (i think) qplot's generic Y conditional on X input
form. Se below.

# Some data:
a <- rnorm(100)
b <- rnorm(100,1,2)
c <- rnorm(100,2,0.5)
# normal boxplot of a,b,c
boxplot(a,b,c) # Looks good
library(ggplot2) # loads qqplot2
# Tries do replicate the simple boxplot
qplot(a,b,c, geom="boxplot") # Not good
# Workaround
d <- c(a,b,c)
e <- c(rep("a",100),rep("b",100),rep("c",100))
qplot(e,d,geom="boxplot") # Works - but there must be a simpler way?

What is the simple to compare multiple variables like this?

thanks in advance

Dear Andreas,

melt() and cast() are nice tools for this kind of problems. They both
reside in the reshape package that automatic loaded when ggplot2 is.

a <- rnorm(100)
b <- rnorm(100,1,2)
c <- rnorm(100,2,0.5)
ds <- data.frame(a = a, b = b, c = c)
library(ggplot2) # loads qqplot2
ggplot(melt(ds), aes(x = variable, y = value)) + geom_boxplot()

HTH,

Thierry


------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Andreas Christoffersen
Verzonden: dinsdag 21 april 2009 16:42
Aan: r-help at r-project.org
Onderwerp: [R] ggplot2 - boxplot of variables / columns

Hi,

ggplot/qplot is great - it has really helped me do some nice things.
However, simple boxplot of different columns/variables is a bit
tricky, because of (i think) qplot's generic Y conditional on X input
form. Se below.

# Some data:
a <- rnorm(100)
b <- rnorm(100,1,2)
c <- rnorm(100,2,0.5)
# normal boxplot of a,b,c
boxplot(a,b,c) # Looks good
library(ggplot2) # loads qqplot2
# Tries do replicate the simple boxplot
qplot(a,b,c, geom="boxplot") # Not good
# Workaround
d <- c(a,b,c)
e <- c(rep("a",100),rep("b",100),rep("c",100))
qplot(e,d,geom="boxplot") # Works - but there must be a simpler way?

What is the simple to compare multiple variables like this?

thanks in advance

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On Apr 21, 2009, at 10:42 AM, Andreas Christoffersen wrote:
> Hi,
>
> ggplot/qplot is great - it has really helped me do some nice things.
> However, simple boxplot of different columns/variables is a bit
> tricky, because of (i think) qplot's generic Y conditional on X input
> form. Se below.
>
> # Some data:
> a <- rnorm(100)
> b <- rnorm(100,1,2)
> c <- rnorm(100,2,0.5)
> # normal boxplot of a,b,c
> boxplot(a,b,c) # Looks good
> library(ggplot2) # loads qqplot2
> # Tries do replicate the simple boxplot
> qplot(a,b,c, geom="boxplot") # Not good
> # Workaround
> d <- c(a,b,c)
> e <-
c(rep("a",100),rep("b",100),rep("c",100))
> qplot(e,d,geom="boxplot") # Works - but there must be a simpler
way?
qplot(ind, values, data=stack(data.frame(a,b,c)), geom="boxplot")

I first tried stack(list(a,b,c)) but did not get the expected results.  
If anyone wants to enlighten me on why, I would be happy to offer a  
rewrite of the stack help page that clarifies my inability to parse it  
correctly in its current incarnation.
>
> What is the simple to compare multiple variables like this?
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

David, you solution
> qplot(ind, values, data=stack(data.frame(a,b,c)), geom="boxplot")
Works a treat - thank you!

Thierry, your solution
> ds <- data.frame(a = a, b = b, c = c)
> library(ggplot2) # loads qqplot2
> ggplot(melt(ds), aes(x = variable, y = value)) + geom_boxplot()
Also works.

I can even combine the two solutions, using stack / melt interchangeably.

I am very glad that today I both learned melt/stack and Thierry has
made me curious as to the finer ggplots fine tuning wizardry in ggplot
vs. the simple qplot.

Again - thx.