R:将函数应用于以向量元素作为参数的矩阵 [英] R: Apply function to matrix with elements of vector as argument

问题描述

假设我想对矩阵的每一行应用一个函数.该函数的参数之一采用向量.我想将向量的第一个元素应用于第一行，将第二个元素应用于第二行，依此类推.

Suppose I want to apply a function to each row of a matrix. One of the function's arguments takes a vector. I would like to apply the first element of the vector to the first row, the second element to the second row, etc.

例如:

set.seed(123)
df<-matrix(runif(100), ncol=10)

var2 <- c(1:10)

MYFUNC <- function(x, Var=NA){ 
  sum(x)/Var 
}

我试过了:

apply(df, 1, function(x) MYFUNC(x, Var=var2))

但是这给了我一个 10x10 的矩阵，其中的函数应用于每一行 &Var 组合，而我只对对角线元素感兴趣.我还研究了 mapply 函数，但我不确定如何在这种情况下应用它.

But that gives me a 10x10 matrix with the function applied to each row & Var combination, whereas I'm only interested in the diagonal elements. I also looked into the mapply function, but I'm not sure how to apply it in this case.

任何帮助将不胜感激.

推荐答案

Mapply 绝对是一种可能.这应该有效:

Mapply is definitely a possibility. This should work:

mapply(MYFUNC, x = as.data.frame(t(df)), Var = var2)

#V1        V2        V3        V4        V5        V6        V7        V8        V9       V10 
#5.0795111 2.8693537 1.8285747 1.3640238 0.8300597 0.6280441 0.7706310 0.6720132 0.5719003 0.4259674 

我认为您遇到的问题是 mapply 接受向量或列表.在 R 中，矩阵不是列表，但 data.frame 是.您需要做的就是转置您的矩阵并转换为 data.frame 然后 mapply 应该可以工作.data.frame 中的每一列都是列表中的一个元素，这就是我们必须对其进行转置的原因(以便每个 row 将映射到向量中的每个元素).

The issue I think you were running into is that mapply takes either vectors or lists. In R matrices aren't lists, but data.frames are. All you need to do is transpose your matrix and convert to a data.frame and then mapply should work. Each column in a data.frame is an element in the list which is why we have to transpose it (so that each row will be mapped to each element in the vector).

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