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rcombn

List of all combinations of a minimum value using combn

Here is my data:

      [,1] [,2] [,3]
[1,]    2    3    4
[2,]    2    3    5
[3,]    2    3    6
[4,]    2    4    5
[5,]    2    4    6
[6,]    2    4    2
[7,]    2    4    4
[8,]    2    4    9
[9,]    2    4    10
[10,]   2    4    3

How would I find all combinations of column 3 that are greater than 25? I am struggling how to use the combn function as the help function doesn't seem too intuitive.

Solution

  • If you want a non-loop version:

    x <- read.table(text="2    3    4
2    3    5
2    3    6
2    4    5
2    4    6
2    4    2
2    4    4
2    4    9
2    4    10
2    4    3",stringsAsFactors=FALSE, header=FALSE)

res <- Map(combn, list(x[,3]), seq_along(x[,3]), simplify = FALSE)
unlist(res, recursive = FALSE)[lapply(unlist(res, recursive = FALSE),sum)>=25]

[[1]]
[1]  6  9 10

[[2]]
[1]  6  9 10

[[3]]
[1]  4  5  6 10
...
[[613]]
[1]  4  6  5  6  2  4  9 10  3

[[614]]
[1]  5  6  5  6  2  4  9 10  3

[[615]]
 [1]  4  5  6  5  6  2  4  9 10  3

    EDIT To return rownames instead of the number vector:

    rownames(x) <- paste0("row",1:10)
res <- list(Map(combn, list(x[,3]), seq_along(x[,3]), simplify = FALSE),
 Map(combn, list(rownames(x)), seq_along(rownames(x)), simplify = FALSE))
unlist(res[[2]], recursive = FALSE)[lapply(unlist(res[[1]], recursive = FALSE),sum)>=25]

[[1]]
[1] "row3" "row8" "row9"

[[2]]
[1] "row5" "row8" "row9"

[[3]]
[1] "row1" "row2" "row3" "row9"
...
[[613]]
[1] "row1"  "row3"  "row4"  "row5"  "row6"  "row7"  "row8"  "row9"  "row10"

[[614]]
[1] "row2"  "row3"  "row4"  "row5"  "row6"  "row7"  "row8"  "row9"  "row10"

[[615]]
 [1] "row1"  "row2"  "row3"  "row4"  "row5"  "row6"  "row7"  "row8"  "row9"  "row10"

    EDIT2 To get the elements of the list that match the minimum sum, in this case 25. This gives you the 42 combinations that sum to 25.

    res <- Map(combn, list(x[,3]), seq_along(x[,3]), simplify = FALSE)
res3 <- unlist(res, recursive = FALSE)[lapply(unlist(res, recursive = FALSE),sum)>=25]
res3[which(rapply(res3,sum)==min(rapply(res3,sum)))]

    To get the corresponding rownames as asked before:

    rownames(x) <- paste0("row",1:10)
res4 <- list(Map(combn, list(x[,3]), seq_along(x[,3]), simplify = FALSE),
            Map(combn, list(rownames(x)), seq_along(rownames(x)), simplify = FALSE))
unlist(res4[[2]], recursive = FALSE)[lapply(unlist(res4[[1]], recursive = FALSE),sum)>=25][which(rapply(res3,sum)==min(rapply(res3,sum)))]