将函数族应用于具有多个参数的函数 [英] Apply family of functions for functions with multiple arguments

问题描述

我想使用 apply 系列(在 R 中)中的一个函数来将具有两个参数的函数应用于两个矩阵.我认为这是可能的.我对么?否则，我似乎必须将两个矩阵合二为一，并根据新矩阵重新定义我的函数.

I would like to use a function from the apply family (in R) to apply a function of two arguments to two matrices. I assume this is possible. Am I correct? Otherwise, it would seem that I have to put the two matrices into one, and redefine my function in terms of the new matrix.

这是我想做的一个例子:

Here's an example of what I'd like to do:

a <- matrix(1:6,nrow = 3,ncol = 2)
b <- matrix(7:12,nrow = 3,ncol = 2)

foo <- function(vec1,vec2){
    d <- sample(vec1,1)
    f <- sample(vec2,1)
    result <- c(d,f)
return(result)
}

我想将 foo 应用到 a 和 b.

I would like to apply foo to a and b.

推荐答案

(严格回答问题，而不是为您提供更好的方法供您在此处特别使用....)

(Strictly answering the question, not pointing you to a better approach for you particular use here....)

mapply 是 *apply 函数系列中的函数，用于在循环多个参数时应用函数.

mapply is the function from the *apply family of functions for applying a function while looping through multiple arguments.

因此，您在这里要做的是将每个矩阵转换为包含其行或列的向量列表(您没有指定).有很多方法可以做到这一点，我喜欢使用以下功能:

So what you want to do here is turn each of your matrices into a list of vectors that hold its rows or columns (you did not specify). There are many ways to do that, I like to use the following function:

split.array.along <- function(X, MARGIN) {
    require(abind)
    lapply(seq_len(dim(X)[MARGIN]), asub, x = X, dims = MARGIN)
}

然后你所要做的就是运行:

Then all you have to do is run:

mapply(foo, split.array.along(a, 1),
            split.array.along(b, 1))

与 sapply 一样，mapply 会尽可能将您的输出放入数组中.如果您更喜欢输出为列表，请将 SIMPLIFY = FALSE 添加到 mapply 调用，或者等效地，使用 Map 函数:

Like sapply, mapply tries to put your output into an array if possible. If instead you prefer the output to be a list, add SIMPLIFY = FALSE to the mapply call, or equivalently, use the Map function:

Map(foo, split.array.along(a, 1),
         split.array.along(b, 1))

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