combn dataframe R for 1 variable only

Question

I have a data.frame with the following structure:

x1 x2 x3 x4 x5 x6
 y  n  y  n  n  y
 n  n  y  n  n  y
 y  y  y  y  y  n

I want to make combinations combn() but using only for only 1 of the variable, I mean, gettingthis result:

x1 x2
x1 x3
x1 x4
x1 x5
x1 x6

Instead of: (there are too many varibales that I dont need, and I want to choose the x[i])

x1 x2
...
x2 x1
x2 x2
...
x6 x5

Thank you

Maybe `reshape2::melt(your_data, id.vars = "x1")`? I'm a bit confused about what you want to happen to your `y` and `n` values — Gregor Thomas, Dec 17 '15 at 20:16
Or perhaps just `cbind(names(your_df)[1], names(your_df)[-1])`? — Gregor Thomas, Dec 17 '15 at 20:18
Right, but they are completely absent in your output. Do you want them discarded like that? If so, why are they in your question at all? Does it matter that you have a data frame or is it just the vector of names that you want to work with? — Gregor Thomas, Dec 17 '15 at 20:19
They do matter, but i Want to create a new df with only 2 of those vectors. — Ochetski, Dec 17 '15 at 20:22

score 1 · Answer 1 · answered Dec 17 '15 at 20:29

Using this data

your_data = structure(list(x1 = structure(c(2L, 1L, 2L), .Label = c("n", 
"y"), class = "factor"), x2 = structure(c(1L, 1L, 2L), .Label = c("n", 
"y"), class = "factor"), x3 = structure(c(1L, 1L, 1L), .Label = "y", class = "factor"), 
    x4 = structure(c(1L, 1L, 2L), .Label = c("n", "y"), class = "factor"), 
    x5 = structure(c(1L, 1L, 2L), .Label = c("n", "y"), class = "factor"), 
    x6 = structure(c(2L, 2L, 1L), .Label = c("n", "y"), class = "factor")), .Names = c("x1", 
"x2", "x3", "x4", "x5", "x6"), class = "data.frame", row.names = c(NA, 
-3L))

This matches the output you ask for:

cbind(names(your_data)[1], names(your_data)[-1])
#      [,1] [,2]
# [1,] "x1" "x2"
# [2,] "x1" "x3"
# [3,] "x1" "x4"
# [4,] "x1" "x5"
# [5,] "x1" "x6"

It's a matrix, but you could easily convert to data frame with as.data.frame. You could also functionalize it based on the column number you want in the first position.

single_combn = function(vec, pos) {
    cbind(vec[pos], vec[-pos])
}

Use example:

single_combn(names(your_data), 1)
#      [,1] [,2]
# [1,] "x1" "x2"
# [2,] "x1" "x3"
# [3,] "x1" "x4"
# [4,] "x1" "x5"
# [5,] "x1" "x6"

single_combn(names(your_data), 3)
#      [,1] [,2]
# [1,] "x3" "x1"
# [2,] "x3" "x2"
# [3,] "x3" "x4"
# [4,] "x3" "x5"
# [5,] "x3" "x6"

combn dataframe R for 1 variable only

1 Answers1