CODEWITHSUNDEEP
r
Min
Min

Reputation: 179

Find all combinations of one column based on the unique values of another column in a dataframe

Suppose that I have a dataframe

data.frame(v1 = c(1,1,1,2,2,3), v2 = c(6,1,6,3,4,2))
  v1 v2
1  1  6
2  1  1
3  1  6
4  2  3
5  2  4
6  3  2

Is there an R function to return the following dataframe? i.e. the combinations of v2 with based on the unique values of v1

data.frame(v1 = rep(1:3, 6), v2 = c(6,3,2, 6,4,2, 1,3,2, 1,4,2, 6,3,2, 6,4,2))

   v1 v2
1   1  6
2   2  3
3   3  2
4   1  6
5   2  4
6   3  2
7   1  1
8   2  3
9   3  2
10  1  1
11  2  4
12  3  2
13  1  6
14  2  3
15  3  2
16  1  6
17  2  4
18  3  2

P.S. I don't think my question is duplicated. Here v2 has duplicated values and the output dataframe has to keep the order (i.e. v1 = c(1,2,3, 1,2,3, ...). The desired out put has 18 rows but expand.grid gives 36 rows and crossing gives 15 rows

Upvotes: 1

Views: 228

Answers (1)

ThomasIsCoding
ThomasIsCoding

Reputation: 102900

Try the code below

dfout <- data.frame(
  v1 = unique(df$v1),
  v2 = c(t(rev(expand.grid(rev(with(df, split(v2, v1)))))))
)

which gives

> dfout
   v1 v2
1   1  6
2   2  3
3   3  2
4   1  6
5   2  4
6   3  2
7   1  1
8   2  3
9   3  2
10  1  1
11  2  4
12  3  2
13  1  6
14  2  3
15  3  2
16  1  6
17  2  4
18  3  2

Upvotes: 2

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