将函数应用于矩阵或数据框的每一行

问题描述

假设我有一个 n × 2 矩阵和一个将 2 向量作为其参数之一的函数.我想将该函数应用于矩阵的每一行并获得一个 n 向量.如何在 R 中做到这一点?

Suppose I have a n by 2 matrix and a function that takes a 2-vector as one of its arguments. I would like to apply the function to each row of the matrix and get a n-vector. How to do this in R?

例如，我想计算三个点上的二维标准正态分布的密度:

For example, I would like to compute the density of a 2D standard Normal distribution on three points:

bivariate.density(x = c(0, 0), mu = c(0, 0), sigma = c(1, 1), rho = 0){
    exp(-1/(2*(1-rho^2))*(x[1]^2/sigma[1]^2+x[2]^2/sigma[2]^2-2*rho*x[1]*x[2]/(sigma[1]*sigma[2]))) * 1/(2*pi*sigma[1]*sigma[2]*sqrt(1-rho^2))
}

out <- rbind(c(1, 2), c(3, 4), c(5, 6))

如何将函数应用到out的每一行?

How to apply the function to each row of out?

如何以您指定的方式将除指向函数之外的其他参数的值传递给函数?

How to pass values for the other arguments besides the points to the function in the way you specify?

推荐答案

您只需使用 apply() 函数:

R> M <- matrix(1:6, nrow=3, byrow=TRUE)
R> M
     [,1] [,2]
[1,]    1    2
[2,]    3    4
[3,]    5    6
R> apply(M, 1, function(x) 2*x[1]+x[2])
[1]  4 10 16
R>

这需要一个矩阵并对每一行应用一个(愚蠢的)函数.您将额外的参数作为第四个、第五个、...参数传递给 apply().

This takes a matrix and applies a (silly) function to each row. You pass extra arguments to the function as fourth, fifth, ... arguments to apply().

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