CODEWITHSUNDEEP
r
Newbie1971
Newbie1971

Reputation: 5

R - Permutations between 2 or more vectors, with constraints

I would like to generate all possible permutations between 2 or more vectors, but;

  1. Order is important.
  2. The first number must be lesser than the second, and the second must be lesser than the third.
  3. There cannot be the same number.

For instance:

a <- c(3, 5, 8)
b <- c(8, 10, 12)
c <- c(12, 15, 20)

The first element is from a, the second from b and the third from c.
Possible results would be:

(3, 8, 12), (3, 8, 15), (3, 8, 20), (3, 10, 12), (3, 10, 15) and (3, 10, 20).

But there shouldn't be results with repeated numbers, for instance:

(8, 8, 12), (8, 12, 12).

How can this be accomplished using R?

Upvotes: 0

Views: 265

Answers (1)

jlhoward
jlhoward

Reputation: 59365

If I understand your rules correctly, this should work.

a <- c(3, 5, 8)
b <- c(8, 10, 12)
c <- c(12, 15, 20)

f <- function(x,y) lapply(y[y>tail(x,1)], function(zz) c(x,zz))
g <- function(x,y) unlist(lapply(x,f,y=y), recursive=FALSE)

do.call(rbind,g(g(a,b),c))
#       [,1] [,2] [,3]
#  [1,]    3    8   12
#  [2,]    3    8   15
#  [3,]    3    8   20
#  [4,]    3   10   12
#  [5,]    3   10   15
#  [6,]    3   10   20
#  [7,]    3   12   15
#  [8,]    3   12   20
#  [9,]    5    8   12
# [10,]    5    8   15
# [11,]    5    8   20
# [12,]    5   10   12
# [13,]    5   10   15
# [14,]    5   10   20
# [15,]    5   12   15
# [16,]    5   12   20
# [17,]    8   10   12
# [18,]    8   10   15
# [19,]    8   10   20
# [20,]    8   12   15
# [21,]    8   12   20

For 4 vectors, you would use 

do.call(rbind,g(g(g(a,b),c),d))

and so on.

Upvotes: 1

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