[R] More elegant way of excluding rows with equal values in any 2 columns?

[Dimitris Rizopoulos]

one way is the following:

index <- expand.grid(1:4, 1:4, 1:4, 1:4)

mat <- data.matrix(index)
keep <- apply(mat, 1, function (x, d)
     length(unique(x)) == d, d = ncol(mat))
index[keep, ]


I hope it helps.

Best,
Dimitris


Dimitri Liakhovitski wrote:
> Hello, dear R-ers!
> 
> I built a data frame "grid" (below) with 4 columns. I want to exclude
> all rows that have equal values in ANY 2 columns. Here is how I am
> doing it:
> 
> index<-expand.grid(1:4,1:4,1:4,1:4)
> dim(index)
> # Deleting rows that have identical values in any two columns (1 line of code):
> index<-index[!(index$Var1==index$Var2)&!(index$Var1==index$Var3)&!(index$Var1==index$Var4)&!(index$Var2==index$Var3)&!(index$Var2==index$Var4)&!(index$Var3==index$Var4),]
> dim(index)
> index
> 
> 
> I was wondering if there is a more elegant way of doing it - because
> as the number of columns increases, the amount of code one would have
> to write increases A LOT.
> 
> Thank you very much for any suggestion!
> 
> 
> 

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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