检查矩阵行是否等于R中的向量 [英] check whether matrix rows equal a vector in R , vectorized

问题描述

我很惊讶没有提出这个问题，也许答案会弄清楚为什么.我想将矩阵的行与向量进行比较，并返回是否行==向量到处都是.请参见下面的示例.我想要一个矢量化的解决方案，没有任何应用函数，因为矩阵太大，无法进行慢速循环.假设还有很多行，所以我要避免重复向量.

I'm very surprised this question has not been asked, maybe the answer will clear up why. I want to compare rows of a matrix to a vector and return whether the row == the vector everywhere. See the example below. I want a vectorized solution, no apply functions because the matrix is too large for slow looping. Suppose there are many rows as well, so I would like to avoid repping the vector.

set.seed(1)

M = matrix(rpois(50,5),5,10)

v = c(3 ,   2 ,   7  ,  7 ,   4   , 4   , 7  ,  4  ,  5, 6)

M
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    4    8    3    5    9    4    5    6    7     7
[2,]    4    9    3    6    3    1    5    7    6     1
[3,]    5    6    6   11    6    4    5    2    7     5
[4,]    8    6    4    4    3    8    3    6    5     6
[5,]    3    2    7    7    4    4    7    4    5     6

输出应为

FALSE  FALSE FALSE FALSE TRUE

推荐答案

一种可能性是

rowSums(M == v[col(M)]) == ncol(M)
## [1] FALSE FALSE FALSE FALSE  TRUE

或者类似地

rowSums(M == rep(v, each = nrow(M))) == ncol(M)
## [1] FALSE FALSE FALSE FALSE  TRUE

或

colSums(t(M) == v) == ncol(M)
## [1] FALSE FALSE FALSE FALSE  TRUE

v[col(M)]是rep(v, each = nrow(M))的较短版本，它创建一个与M大小相同的向量(矩阵只是一个向量，请尝试c(M))，然后使用.幸运的是，==是具有array方法的通用函数(请参见methods("Ops")和is.array(M))，该方法允许我们在其上运行rowSums(或colSums)以确保我们有足够的数量匹配为ncol(M)

v[col(M)] is just a shorter version of rep(v, each = nrow(M)) which creates a vector the same size as M (matrix is just a vector, try c(M)) and then compares each element against its corresponding one using ==. Fortunately == is a generic function which has an array method (see methods("Ops") and is.array(M)) which allows us to run rowSums (or colSums) on it in order to makes sure we have the amount of matches as ncol(M)

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