R-从给定约束的2个向量生成所有组合 [英] R - generate all combinations from 2 vectors given constraints
问题描述
在给定两个约束的情况下，我想生成两个向量的所有组合：第一个向量的字符数不能超过3个，第二个向量的字符数必须始终至少一个。我还想更改组合中字符的最终数量。
I would like to generate all combinations of two vectors, given two constraints: there can never be more than 3 characters from the first vector, and there must always be at least one characters from the second vector. I would also like to vary the final number of characters in the combination.
例如，这是两个向量：
vec1=c("A","B","C","D")
vec2=c("W","X","Y","Z")
说我想要组合三个字符。可能的可接受排列是： A B X 或 A Y Z 。不能接受的排列是： A B C ，因为 vec2 。
Say I wanted 3 characters in the combination. Possible acceptable permutations would be: "A" "B" "X"or "A" "Y" "Z". An unacceptable permutation would be: "A" "B" "C" since there is not at least one character from vec2.
现在说我要组合5个字符。可能的可接受排列是： A C Z Y 或 A Y Z X 。不能接受的排列是： A C D B X ，因为 vec2中有> 3个字符。
Now say I wanted 5 characters in the combination. Possible acceptable permutations would be: "A" "C" "Z" "Y" or "A" "Y" "Z" "X". An unacceptable permutation would be: "A" "C" "D" "B" "X" since there are >3 characters from vec2.
我想我可以使用 expand.grid 生成所有组合，然后以某种方式子集，但必须有一种更简单的方法。
I suppose I could use expand.grid to generate all combinations and then somehow subset, but there must be an easier way. Thanks in advance!
推荐答案
我不确定这样做是否更容易，但是您可以放弃不满足您需求的排列方式此策略的条件：
I'm not sure wheter this is easier, but you can leave away permutations that do not satisfy your conditions whith this strategy:
-
从
vec1生成所有组合
从 vec2 生成所有可接受的组合。
generate all combinations from vec2 that are acceptable.
生成所有组合，并从1中提取一个解决方案。从2中提取一个解决方案。在此之后，我将使用条件3进行过滤。
generate all combinations taking one solution from 1. + one solution from 2. Here I'd do the filtering with condition 3 afterwards.
（如果您正在寻找组合，请完成，否则：）在每个结果中生成字母的所有排列。
(if you're looking for combinations, you're done, otherwise:) produce all permutations of letters within each result.
现在，让我们来
vec1 <- LETTERS [1:4]
vec2 <- LETTERS [23:26]
## lists can eat up lots of memory, so use character vectors instead.
combine <- function (x, y)
combn (y, x, paste, collapse = "")
res1 <- unlist (lapply (0:3, combine, vec1))
res2 <- unlist (lapply (1:length (vec2), combine, vec2))
现在我们有：
> res1
[1] "" "A" "B" "C" "D" "AB" "AC" "AD" "BC" "BD" "CD" "ABC"
[13] "ABD" "ACD" "BCD"
> res2
[1] "W" "X" "Y" "Z" "WX" "WY" "WZ" "XY" "XZ" "YZ"
[11] "WXY" "WXZ" "WYZ" "XYZ" "WXYZ"
res3 <- outer (res1, res2, paste0)
res3 <- res3 [nchar (res3) == 5]
所以您在这里：
> res3
[1] "ABCWX" "ABDWX" "ACDWX" "BCDWX" "ABCWY" "ABDWY" "ACDWY" "BCDWY" "ABCWZ"
[10] "ABDWZ" "ACDWZ" "BCDWZ" "ABCXY" "ABDXY" "ACDXY" "BCDXY" "ABCXZ" "ABDXZ"
[19] "ACDXZ" "BCDXZ" "ABCYZ" "ABDYZ" "ACDYZ" "BCDYZ" "ABWXY" "ACWXY" "ADWXY"
[28] "BCWXY" "BDWXY" "CDWXY" "ABWXZ" "ACWXZ" "ADWXZ" "BCWXZ" "BDWXZ" "CDWXZ"
[37] "ABWYZ" "ACWYZ" "ADWYZ" "BCWYZ" "BDWYZ" "CDWYZ" "ABXYZ" "ACXYZ" "ADXYZ"
[46] "BCXYZ" "BDXYZ" "CDXYZ" "AWXYZ" "BWXYZ" "CWXYZ" "DWXYZ"
如果您希望将结果分成单个字母：
If you prefer the results split into single letters:
res <- matrix (unlist (strsplit (res3, "")), nrow = length (res3), byrow = TRUE)
> res
[,1] [,2] [,3] [,4] [,5]
[1,] "A" "B" "C" "W" "X"
[2,] "A" "B" "D" "W" "X"
[3,] "A" "C" "D" "W" "X"
[4,] "B" "C" "D" "W" "X"
（剪切）
[51,] "C" "W" "X" "Y" "Z"
[52,] "D" "W" "X" "Y" "Z"
以下是您的组合。
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