Convert ppp object to multitpe object

Question

I am working on spatial point pattern analysis using R.

I have two sets of coordinates, both defined inside a 32*20 region. I first convert two data sets to ppp objects:

Tumor_CD8 <- ppp(Tumor_CD8[,1],Tumor_CD8[,2], c(0,32), c(0,20))
Tumor_CD3 <- ppp(Tumor_CD3[,1],Tumor_CD3[,2], c(0,32), c(0,20))

And now I am confused about how to combine them to a multitype point pattern object, in order to perform functions like: Gcross, Kcross and Lcross, etc.

Answer 1

Construct a new ppp using the coordinates of the components. Create a marks parameter as a factor of the same length as the sum of both ppp sizes:

> p1 = ppp(runif(10),runif(10))
> p2 = ppp(runif(10),runif(10))
> pm = ppp(c(p1$x, p2$x),c(p1$y,p2$y), 
           marks=factor(c(rep("A",p1$n),rep("B",p2$n))))
> is.multitype(pm)
[1] TRUE
> plot(pm)

should plot different markers for each type. Note it has to be a factor - numeric or character will create something with marks but is.multitype is FALSE unless its a factor.

Specify a window as well if not using the default (0,1) square.