Question

假设我有两个向量。

v1<-c("a","b","c")
v2<-c("x","y","z")

我想要的是一个组合向量，它从一个到另一个完全交叉。但在此之前，载体中的每个元素都需要重复3次。

我想得到的最终载体是

a a a x x x a a a y y y a a a z z z b b b x x x b b b y y y .....

除了for-loop之外，是否有一种简单的方法可以使上面的矢量？

Answer 1

使用rep：

#first, create necessary repeats in the two vectors in order to make one cross-product vector
v1_r <- rep(v1, each=3)
v2_r <- rep(v2, 3)
#combine them into one vector
v3 <- as.vector(rbind(v1_r,v2_r))
#add another repeat
v3_r <- rep(v3,each=3)

> v3_r
 [1] "a" "a" "a" "x" "x" "x" "a" "a" "a" "y" "y" "y" "a" "a"
[15] "a" "z" "z" "z" "b" "b" "b" "x" "x" "x" "b" "b" "b" "y"
[29] "y" "y" "b" "b" "b" "z" "z" "z" "c" "c" "c" "x" "x" "x"
[43] "c" "c" "c" "y" "y" "y" "c" "c" "c" "z" "z" "z"

一行中的所有步骤：

v3_r <- rep(as.vector(rbind(rep(v1, each=3),rep(v2,3))),each=3)

Answer 2

使用dplyr包来替代@Heroka的替代方法。

v1<-c("a","b","c")
v2<-c("x","y","z")


library(dplyr)

data.frame(expand.grid(v1,v2)) %>%        # create all combinations
  mutate_each(funs(as.character)) %>%     # transform to character
  arrange(Var1) %>%                       # order by first column
  rowwise() %>%                           # for each row
  do(data.frame(vec=c(rep(.$Var1,3), rep(.$Var2,3)), stringsAsFactors=F))   # create a new vector by repeating the first element 3 times and then the second 3 times


#    vec
# 1    a
# 2    a
# 3    a
# 4    x
# 5    x
# 6    x
# 7    a
# 8    a
# 9    a
# 10   y
# .. ...

不确定为什么更喜欢使用包而不是基础R，但以防其他人有类似问题（作为更大进程的一部分）并且他想使用dplyr方法。

用r中的两个向量完全交叉的元素创建一个向量

2 个答案: