[R] List of "occurrence" matrices

[Dan Davison]

Lauri Nikkinen wrote:
> 
> R users,
> 
> I don't know if I can make myself clear but I'll give it a try. I have
> a data.frame like this
> 
> x <- "var1,var2,var3,var4
> a,b,b,a
> b,b,c,b
> c,a,a,a
> a,b,c,c
> b,a,c,a
> c,c,b,b
> a,c,a,b
> b,c,a,c
> c,a,b,c"
> DF <- read.table(textConnection(x),  header=T, sep=",")
> DF
> 
> and I would like to sum all the combinations/occurences by a factor
> (letter in this case) between variables and produce a list of
> "occurrence" matrices. For example in this case the "occurrence"
> matrix (first element of list) for factor "a" should look like this
> 
>>occulist
> $a
> 	var1	var2	var3	var4
> var1	x	0	1	1
> var2	0	x	1	2
> var3	1	1	x	1
> var4	1	2	1	x
> 
> $b
> etc.
> 
> because there is two rows where var2 and var4 has "a"
> 
> 
> I think this does it:
> 
> occur.matrices <- function(df) {
>     levels <- levels(unlist(df))
>     ans <- lapply(levels, function(level) crossprod(df == level))
>     structure(ans, names=levels)
> }
> 
> Dan
> 
>> occur.matrices(DF)
> $a
>      var1 var2 var3 var4
> var1    3    0    1    1
> var2    0    3    1    2
> var3    1    1    3    1
> var4    1    2    1    3
> 
> $b
>      var1 var2 var3 var4
> var1    3    1    0    1
> var2    1    3    1    1
> var3    0    1    3    1
> var4    1    1    1    3
> 
> $c
>      var1 var2 var3 var4
> var1    3    1    0    1
> var2    1    3    0    1
> var3    0    0    3    1
> var4    1    1    1    3
> 
> 
> 
> DF[DF$var2=="a" & DF$var4=="a",]
> 
> Can you give an advice how to achieve this kind of a list of matrices?
> 
> -Lauri
> 
> ______________________________________________
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> 
> 

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