Remove duplicates across columns [duplicate]

Question

df
     [,1] [,2]
 [1,] "a"  "b" 
 [2,] "a"  "c"
 [3,] "a"  "d"
 [4,] "b"  "a"
 [5,] "b"  "c"
 [6,] "b"  "d" 
 [7,] "c"  "a" 
 [8,] "c"  "b" 
 [9,] "c"  "d"

Let's assume have a data.frame like this and I want to remove duplicates in sense of across the column

df1
     [,1] [,2]
 [1,] "a"  "b" 
 [2,] "a"  "c"
 [3,] "a"  "d"
 [5,] "b"  "c"
 [6,] "b"  "d" 
 [9,] "c"  "d"

I want to end up like this.

Answer 1

We can sort the elements in each row with apply, transpose the output, apply duplicated to return a logical vector and use that for subsetting the rows

df[!duplicated(t(apply(df[, 1:2], 1, sort))),]
#     [,1] [,2]
#[1,] "a"  "b" 
#[2,] "a"  "c" 
#[3,] "a"  "d" 
#[4,] "b"  "c" 
#[5,] "b"  "d" 
#[6,] "c"  "d" 

---

or another option is pmin/pmax

df[!duplicated(cbind(pmin(df[,1], df[,2]), pmax(df[,1], df[,2]))),]

data

df <- structure(c("a", "a", "a", "b", "b", "b", "c", "c", "c", "b", 
"c", "d", "a", "c", "d", "a", "b", "d"), .Dim = c(9L, 2L))