强制幻想阵容从特定数量的球队中选择球员？

Question

考虑到R中使用RGLPK的以下幻想曲棍球模型，如何从总共4支队伍中强制选择？我的模特是

num.players <- length(players[,1])
f <- players$proj
var.types <- rep("B", num.players)
A <- rbind(
as.numeric(players$position == "W"),as.numeric(players$position == "W"),
as.numeric(players$position == "C"),as.numeric(players$position == "C"),
as.numeric(players$position == "D"),as.numeric(players$position == "D"),
as.numeric(players$position == "G"),
as.numeric(players$position %in% c("W","C","D","G")),
players$salary)
dir <- c(
">=","<=",
">=","<=",
">=","<=",
"==",
"==",
"<=")
b <- c(
3,4,
2,3,
2,3,
1,
9,
50000)
sol <- Rglpk_solve_LP(obj = f, mat = A, dir = dir, rhs = b,                      types = var.types, max = TRUE)

我尝试添加以下约束

length(unique(players$team)),
"==",
4,

这个约束总是正确的，因为我的数据有14个团队，而且长度（独特（玩家$ team））使用整个数据集而不仅仅是选定的玩家。