# Playing cards, with R

May 11, 2013
By

(This article was first published on Freakonometrics » R-english, and kindly contributed to R-bloggers)

In my courses on R, I usually show how to insert a picture as a background for a graph. But it is also to see the picture as an object, and to insert it in a graph everywhere we like to see it, as explained on the awesome blog http://rsnippets.blogspot.ca/…. (in a post published in January 2012). I wanted to insert cards in a graph. Cards can be found, e.g. on wikipedia, even French versions, like the one I used to play with when I was a kid (see e.g. the Jack of clubs, http://commons.wikimedia.org/…, or the Queen of hearts, http://commons.wikimedia.org/…). But graphs are in svg. First, we have to export them in ppm, either using gimp, or online, with http://www.sciweavers.org/… instance. Here, I have a copy of the 32 cards, and the code to read one, in R, is

library(pixmap)
card=read.pnm("1000px_10_of_clubs.ppm")

Then, I can plot the cart using

plot(card,add=TRUE)

(on a predefined graph) The interesting part is that it is possible to plot the picture within a given box, but it has be bee specified when we read the image file, using

card=read.pnm("1000px_10_of_clubs.ppm",bbox=c(300,200,800,1100))
plot(card,add=TRUE)

If we want to visulize all the cards, first, we have to store the pictures (the cards) in some R format, in a list, then to check for all of them for their dimensions, and then, we can write a code to plot any of them, anywhere we like (again it has to be specified when we read the file, which might take a while)

L=list(cards="french cards")
L2=list(cards="french cards")
nb=c("07","08","09","10","Jack","Queen","King","01")
N=1:32
for(n in N){
i=trunc((n-1)/4)+1  #number
j=(n-1)%%4+1        #color
name_card=paste("1000px_",nb[i],"_of_",color[j],".ppm",sep="")
L2[[n+1]]=name_card
}

Now,if we want to play one specific card (out of those 32), we can use

card_plot=function(id,loc){
usr <- par("usr")
pin <- par("pin")
card=L[[id+1]]
x.asp <- (card@size[2] * (usr[2] - usr[1]) / pin[1])
y.asp <- (card@size[1] * (usr[4] - usr[3]) / pin[2])
card.height <-.9
card.width <- card.height * x.asp / y.asp
y.0 <- loc[2]
x.0 <- loc[1]
bbox <- c(x.0, y.0, x.0 + card.width, y.0 + card.height)
}

Note that, here, first we read the file to check the dimensions, and then, we read it again, using the appropriate box (with height given, here 0.9). Now, it is possible to plot the 32 cards on the same graph, for a given ordering

seq_card_plot=function(seq_id){
X=seq(0,7*.5,by=.5)
Y=0:4
table = plot(0:4,0:4,ylim=c(0,4),
axes=FALSE,xlab="",ylab="",col="white")
for(n in 1:length(seq_id)){
i=trunc((n-1)/4)+1  #number
j=(n-1)%%4+1         #color
card_plot(id=seq_id[n],loc=c(X[i],Y[j]))
}}

If we did not shuffle the cards, it would be

seq_card_plot(N)

But it is possible to shuffle the cards, of course,

set.seed(1)
seq_card_plot(sample(N))

Now, to be honest, I am a bit disappointed because I did not use the fact that I have vector based images here. So it should be possible to get much nicer images, I guess…

### Arthur Charpentier

Arthur Charpentier, professor in Montréal, in Actuarial Science. Former professor-assistant at ENSAE Paristech, associate professor at Ecole Polytechnique and assistant professor in Economics at Université de Rennes 1.  Graduated from ENSAE, Master in Mathematical Economics (Paris Dauphine), PhD in Mathematics (KU Leuven), and Fellow of the French Institute of Actuaries.