粘贴网格-expand.grid用于字符串连接 [英] paste grid -- expand.grid for string concatenation
问题描述
如果要获取两个向量的所有组合，可以使用 rep /回收规则：
If we want to get all combinations of two vectors, we can use rep/recycling rules:
x <- 1:4
y <- 1:2
cbind(rep(x, each = length(y)), rep(y, length(x)))
# [,1] [,2]
# [1,] 1 1
# [2,] 1 2
# [3,] 2 1
# [4,] 2 2
# [5,] 3 1
# [6,] 3 2
# [7,] 4 1
# [8,] 4 2
但是 expand.grid 更好-它为我们处理了所有重复。
But expand.grid is much nicer -- it handles all the repetition for us.
expand.grid(x, y)
# Var1 Var2
# 1 1 1
# 2 2 1
# 3 3 1
# 4 4 1
# 5 1 2
# 6 2 2
# 7 3 2
# 8 4 2
是否有用于连接字符串的简单版本？像 paste.grid 一样？我有一个命名对象，其中很多对象的名称都像 x_y_z ，其中 x ， y 和 z 就像 x 和 y 。
Is there a simple version of this for concatenating strings? Like paste.grid? I have a named object where a lot of the objects have names like x_y_z where x, y, and z vary like x and y above.
例如，假设 x 可以为 avg 或中位数 ， y 可以是男性 或女性 和 z 可以为身高 或体重 。
For example, suppose x can be "avg" or "median", y can be "male" or "female", and z can be "height" or "weight". How can we concisely get all 8 combinations of the three?
使用 rep 是一件很痛苦的事情：
Using rep is a pain:
x <- c("avg", "median")
y <- c("male", "female")
z <- c("height", "weight")
paste(rep(x, each = length(y) * length(z)),
rep(rep(y, each = length(z)), length(x)),
rep(z, length(x) * length(y)), sep = "_")
重新使用 expand.grid 有点笨拙（可能效率很低）：
And repurposing expand.grid is a bit clunky (and probably inefficient):
apply(expand.grid(x, y, z), 1, paste, collapse = "_")
我错过了什么吗？有没有更好的方法？
Am I missing something? Is there a better way to do this?
推荐答案
是的，这就是交互确实
levels(interaction(x,y,z,sep='_'))
实现与您的 rep 代码几乎相同。
The implementation is pretty much the same as your rep code.
输出：
[1] "avg_female_height" "median_female_height" "avg_male_height" "median_male_height" "avg_female_weight"
[6] "median_female_weight" "avg_male_weight" "median_male_weight"
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