[R] Create a list object in a loop

[R. Michael Weylandt]

You are overriding "b" at each loop iteration and consequently only
keeping the last one.

Perhaps

b <- list()

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

Generally it's bad practice to have a dynamically growing object in R
but I think the performance penalty for lists isn't too bad. (Not
verified, I just think I saw that somewhere)

What might be even better:

months <- sort(unique(OT1$month))

b <- vector("list", length(months))
names(b) <- months

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

Michael

On Fri, Mar 9, 2012 at 10:48 AM, Aurelie Cosandey Godin <GodinA at dal.ca> wrote:
> 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!
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