[R] Create a list object in a loop

[Aurelie Cosandey Godin]

Dear all,

I'm trying to create a list of point patterns ppp.object {spatstat} in a loop.
My dataset looks like this:

    > names(OT1);head(OT1);dim(OT1)
    [1] "EID"       "latitude"  "longitude" "month"     "year"      "CPUE"      "TSUM"     
    [8] "fTSUM"    
                    EID latitude longitude month year CPUE TSUM fTSUM
    1   167-1-1996-1135 67.70000 -61.81667     9 1996    0    0     F
    2  167-10-1996-1135 67.71667 -59.18333     9 1996    0    0     F
    3 167-100-1996-1135 67.86667 -59.43333    10 1996    0    0     F
    4 167-101-1996-1135 67.95000 -59.58333    10 1996    0    0     F
    5 167-102-1996-1135 68.10000 -59.76667    10 1996    0    0     F
    6 167-103-1996-1135 67.81667 -59.38333    10 1996    0    0     F
    [1] 2707    8

What I would like to do is to select data for each of my month and create a ppp.object.

    > sort(unique(OT1$month))
    [1]  7  8  9 10 11 12

The following loop works and I can see each of my figures:

    for(i in sort(unique(OT1$month))){ 
      a<-OT1[OT1$month==i,]
      b<-ppp(a$longitude,a$latitude,marks=a$fTSUM,window=newW)
      plot(b,main=i)
    }

How can I access each of my ppp.objects? I've tried adding a list() in the loop command such that I can access the data but without any success... Any help would be much appreciated!

Thank you!