在R中重复一个简单的矩阵算法？ [英] Repeating a simple algorithm for matrices in R?

问题描述

我试图通过创建第一部分来避免重复一些简单的计算。但是我想知道为什么我不能获得与第二部分计算结果相同的结果（第二部分给出了正确答案）？

第一部分：

  a =矩阵（c（8,11,2,6,8） （a）
 mc = colMeans（a）
 nc = ncol（a）
 mc = 
 mr = rowMeans（a）
 gr = mean（a）
 
（m =矩阵（c（a [rep（1：nr，nr） nc，each = nc）]  -  mr [rep（1：nr，nr）]  -  
 mc [rep（1：nc，each = nc）] + gr），nrow = nr，ncol = nc）） ##这是不正确的答案！ 
  

第二部分：

  a11 <-a [1,1] -mr [1] -mc [1] + gr 
 a21 <-a [2,1]  - mr [2] -mc [1] + gr 
 a31 <-a [3,1] -mr [3] -mc [1] + gr 
 a12 <-a [1,2 ] mr [1] -mc [2] + gr 
 a22 <-a [2,2] -mr [2] -mc [2] + gr 
 a32 <-a [3 ，2]  -  mr [3] -mc [2] + gr 
 a13 <-a [1,3] -mr [1] -mc [3] + gr 
 a23 <-a [2,3]  -  mr [2] -mc [3] + gr 
 a33 <-a [3,3] -mr [3] -mc [3] + gr 
 a14< -  a [1,4]  -  mr [1]  -  mc [4] + gr 
 a24 < -  a [2,4]  -  mr [2]  -  mc [4] + gr 
 a34 <  -  a [3,4]  -  mr [3]  -  mc [4] + gr 
 
g = paste0（a，rep（1：3，3） ，每个= 3））
（m =矩阵（c（mget（g）），nr = 3，ncol = 4））##这是正确的答案！ 
  

解决方案

您可以使用 / code>来计算差异：

$ $ $ $ $ $ $ myMat < - a - outer（mr，mc，+ ）+ gr
myMat

[，1] [，2] [，3] [，4]
[1，] 2 1 0 -3
[ 2，] 2 0 -2 0
[3，] -4 -1 2 3


重建m，使它不是一个列表
$ b $ pre $ m $ m = matrix（unlist（mget（g）），nr = 3， ncol = 4）

现在，检查它们是否一致：

 相同（m，myMat）
 [1] TRUE 
  

I'm trying to avoid repeating some simple calculations by creating the first part. But I'm wondering why I don't obtain the same result as calculated by the second part (second part gives the correct answer)?

First part:

 a = matrix(c(8,11,2, 6,8,4, 4,5,6, 2,8,8), nrow = 3)   
nr = nrow(a)
nc = ncol(a)
mc = colMeans(a)
mr = rowMeans(a)
gr = mean(a)

(m = matrix(c(a[rep(1:nr, nr), rep(1:nc, each = nc)] - mr[rep(1:nr, nr)] - 
mc[rep(1:nc, each = nc)] + gr), nrow = nr, ncol = nc))     ## This is NOT correct answer !!

Second part:

a11 <- a[1, 1] - mr[1] - mc[1] + gr
a21 <- a[2, 1] - mr[2] - mc[1] + gr
a31 <- a[3, 1] - mr[3] - mc[1] + gr
a12 <- a[1, 2] - mr[1] - mc[2] + gr
a22 <- a[2, 2] - mr[2] - mc[2] + gr
a32 <- a[3, 2] - mr[3] - mc[2] + gr
a13 <- a[1, 3] - mr[1] - mc[3] + gr
a23 <- a[2, 3] - mr[2] - mc[3] + gr
a33 <- a[3, 3] - mr[3] - mc[3] + gr
a14 <- a[1, 4] - mr[1] - mc[4] + gr
a24 <- a[2, 4] - mr[2] - mc[4] + gr
a34 <- a[3, 4] - mr[3] - mc[4] + gr

g = paste0("a", rep(1:3, 3), rep(1:4, each = 3))
(m = matrix(c(mget(g)), nr = 3, ncol = 4))             ## This is the correct answer !!

解决方案

You can use outer to calculate the differences:

myMat <- a - outer(mr, mc, "+") + gr
myMat

     [,1] [,2] [,3] [,4]
[1,]    2    1    0   -3
[2,]    2    0   -2    0
[3,]   -4   -1    2    3

rebuild m so that it is not a list

m = matrix(unlist(mget(g)), nr = 3, ncol = 4)

Now, check that they are identical:

identical(m, myMat)
[1] TRUE

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