执行矩阵的成对比较

Question

我有一个包含 n 个变量的矩阵，我想创建一个新矩阵，它是每个向量的成对差异，但不是自身。以下是数据示例。

    Transportation.services Recreational.goods.and.vehicles Recreation.services Other.services
         2.958003                     -0.25983789            5.526694           2.8912009
         2.857370                     -0.03425164            5.312857           2.9698044
         2.352275                      0.30536569            4.596742           2.9190123
         2.093233                      0.65920773            4.192716           3.2567390
         1.991406                      0.92246531            3.963058           3.6298314
         2.065791                      1.06120930            3.692287           3.4422340

我尝试在下面运行一个 for 循环，但我知道 R 的循环非常慢。

Difference.Matrix<- function(data){
 n<-2
new.cols="New Columns"
list = list()
for (i in 1:ncol(data)){

    for (j in n:ncol(data)){

        name <- paste("diff",i,j,data[,i],data[,j],sep=".")
        new<- data[,i]-data[,j]
        list[[new.cols]]<-c(name)
        data<-merge(data,new)
        }
    n= n+1
    }
results<-list(data=data)
return(results)
}

正如我之前所说，代码运行速度非常慢，甚至还没有完成一次运行。我也为初学者级别的编码道歉。另外我知道这段代码将原始数据保留在矩阵上，但我可以稍后将其删除。

我可以对这些数据使用 apply 函数或 foreach 吗？

Answer 1

您可以找到带有combn 的对并使用apply 创建结果：

apply(combn(ncol(d), 2), 2, function(x) d[,x[1]] - d[,x[2]])
##          [,1]      [,2]       [,3]      [,4]      [,5]      [,6]
## [1,] 3.217841 -2.568691  0.0668021 -5.786532 -3.151039 2.6354931
## [2,] 2.891622 -2.455487 -0.1124344 -5.347109 -3.004056 2.3430526
## [3,] 2.046909 -2.244467 -0.5667373 -4.291376 -2.613647 1.6777297
## [4,] 1.434025 -2.099483 -1.1635060 -3.533508 -2.597531 0.9359770
## [5,] 1.068941 -1.971652 -1.6384254 -3.040593 -2.707366 0.3332266
## [6,] 1.004582 -1.626496 -1.3764430 -2.631078 -2.381025 0.2500530

您可以使用另一个apply 添加适当的名称。这里的列名很长，这会影响格式，但标签说明了每列的不同之处：

x <- apply(combn(ncol(d), 2), 2, function(x) d[,x[1]] - d[,x[2]])
colnames(x) <- apply(combn(ncol(d), 2), 2, function(x) paste(names(d)[x], collapse=' - '))
> x
     Transportation.services - Recreational.goods.and.vehicles Transportation.services - Recreation.services
[1,]                                                  3.217841                                     -2.568691
[2,]                                                  2.891622                                     -2.455487
[3,]                                                  2.046909                                     -2.244467
[4,]                                                  1.434025                                     -2.099483
[5,]                                                  1.068941                                     -1.971652
[6,]                                                  1.004582                                     -1.626496
     Transportation.services - Other.services Recreational.goods.and.vehicles - Recreation.services
[1,]                                0.0668021                                             -5.786532
[2,]                               -0.1124344                                             -5.347109
[3,]                               -0.5667373                                             -4.291376
[4,]                               -1.1635060                                             -3.533508
[5,]                               -1.6384254                                             -3.040593
[6,]                               -1.3764430                                             -2.631078
     Recreational.goods.and.vehicles - Other.services Recreation.services - Other.services
[1,]                                        -3.151039                            2.6354931
[2,]                                        -3.004056                            2.3430526
[3,]                                        -2.613647                            1.6777297
[4,]                                        -2.597531                            0.9359770
[5,]                                        -2.707366                            0.3332266
[6,]                                        -2.381025                            0.2500530