[R] zeros keep dropping

[Peter Dalgaard]

Lanna Jin wrote:
> Hello All!
> 
> I am trying to plot the frequency of species coocurrance.
> If given a data set similar like this...(V1="species A", V2="species B",
> V3="frequency of cooccurance")
> 
>> data
>   V1 V2 V3
> 1  A  B  0
> 2  A  C  2
> 3  A  D  5
> 4  B  C  0
> 5  B  D  1
> 6  C  D  0
>> data1<-as.data.frame(lapply(data,function(x)(rep(x,data$V3))))
>> as.data.frame(data1[-1])
>> fdata<-ftable(as.data.frame(data1[-3]))
>> fdata
>    V2 B C D
> V1
> A     0 2 5
> B     0 0 1
> C     0 0 0
> 
> Question 1:  How can I create a matrix or (contingency) table that would
> include "A, B, C and D" in columns and "A, B, C, and D" in the rows (through
> R, not manually adjusting the original data text file).
> - When I "lapply(data,function(x)(rep(x,data$V3)))", the rows with V3=0 are
> dropped.
> 
> Question 2: How would I graph the frequency of the counts (V3) (would look
> most likely follow the poisson distribution).
> I've used plot(table(data$V3)) to get the correct graph, but is there a way
> to graph the frequency from a contingency table (question 1) to elicit the
> same graph?
> 
> Thanks in advance for your help...

I think you need an intervening

all.levels <- c("A", "B", "C", "D") # or LETTERS[1:4]
data$V1 <- factor(data$V1, levels=all.levels)
data$V2 <- factor(data$V2, levels=all.levels)

and it is probably better to use something like

data1 <- data[rep(1:6, data$V3),]

That is, if you insist on the strategy of replicating rows.

You may prefer xtabs(V3~V1+V2, data=data).

(In all cases "or something like that". I haven't actually tested.)

-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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