结合两个循环结构以获得矩阵输出 [英] combine two looping structures to obtain a matrix output

问题描述

我在R中使用了两个密切相关的公式.我想知道是否有可能将 B1 和 B2 组合起来以获得我的所需矩阵输出如下所示?

I'm using two closely related formulas in R. I was wondering if it might be possible to combine B1 and B2 to get my desired matrix output shown below?

z <- "group    y1    y2
1 1         2     3
2 1         3     4
3 1         5     4
4 1         2     5
5 2         4     8
6 2         5     6
7 2         6     7
8 3         7     6
9 3         8     7
10 3        10     8
11 3         9     5
12 3         7     6"

dat <- read.table(text = z, header = T)

(B1 = Reduce("+", group_split(dat, group, .keep = FALSE) %>%
  map(~ nrow(.)*(colMeans(.)-colMeans(dat[-1]))^2)))

#     y1       y2 
#61.86667 19.05000

(B2 = Reduce("+",group_split(dat, group, .keep = FALSE) %>%
              map(~ nrow(.)*prod(colMeans(.)-colMeans(dat[-1])))))

# 24.4

所需的矩阵输出:

matrix(c(61.87,24.40,24.40,19.05),2)
#      [,1]  [,2]
#[1,] 61.87 24.40
#[2,] 24.40 19.05

推荐答案

也许像这样吗?

mat <- matrix(B2, length(B1), length(B1))
diag(mat) <- B1
mat
#      [,1]  [,2]
#[1,] 61.87 24.40
#[2,] 24.40 19.05

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