How do I select all unique combinations of two columns in an R data frame?

Question

I have a correlation matrix that I put in a dataframe like so:

row | var1 | var2 | cor
1   | A    | B    | 0.6
2   | B    | A    | 0.6
3   | A    | C    | 0         


        

Answer 1

A dplyr possibility could be:

df %>%
 group_by(grp = paste0(pmin(var1, var2), pmax(var1, var2))) %>%
 slice(1) %>%
 ungroup() %>%
 select(-grp)

    row var1  var2    cor
     
1     1 A     B       0.6
2     3 A     C       0.4

Or:

df %>%
 group_by(grp = paste0(pmin(var1, var2), pmax(var1, var2))) %>%
 filter(row_number() == min(row_number())) %>%
 ungroup() %>%
 select(-grp)

Or:

df %>%
 group_by(grp = paste0(pmin(var1, var2), pmax(var1, var2))) %>%
 summarise_all(list(first)) %>%
 ungroup() %>%
 select(-grp)