R：使用單獨的坐標矩陣訪問矩陣的元素

Question

我有一個矩陣（expTrans），當前填充了零。 我有第二個矩陣（expCoor），其中第二列用列名填充，第三列用行號填充。 我想使用第二個矩陣中的坐標將第一個矩陣中的某些元素更改為1。 當我使用此代碼時，R用1填充提到的每一列中提到的每一行（各列完全相同）：

expTrans<-matrix(0, nrow(cashflows), ncol(dmat))
colnames(expTrans)<-substr(colnames(dmat),4,6)
expTrans[expCoor[,3],colnames(expenses)[expCoor[,1]]]<-1

有沒有一種方法可以只更改每個坐標指定的行和列，而不必遍歷整個矩陣？

這是一個簡單的示例來說明我在說什么：

> m<-matrix(0,ncol=10,nrow=10)
> colnames(m)<-c("a","b","c","d","e","f","g","h","i","j")
> m
      a b c d e f g h i j
 [1,] 0 0 0 0 0 0 0 0 0 0
 [2,] 0 0 0 0 0 0 0 0 0 0
 [3,] 0 0 0 0 0 0 0 0 0 0
 [4,] 0 0 0 0 0 0 0 0 0 0
 [5,] 0 0 0 0 0 0 0 0 0 0
 [6,] 0 0 0 0 0 0 0 0 0 0
 [7,] 0 0 0 0 0 0 0 0 0 0
 [8,] 0 0 0 0 0 0 0 0 0 0
 [9,] 0 0 0 0 0 0 0 0 0 0
[10,] 0 0 0 0 0 0 0 0 0 0
> ind<-cbind(sample(1:10,10),sample(1:10,10), c("a","a","b","j","c","d","e", "a", "b", "b"))
> ind
      [,1] [,2] [,3]
 [1,] "4"  "8"  "a" 
 [2,] "2"  "9"  "a" 
 [3,] "9"  "3"  "b" 
 [4,] "3"  "1"  "j" 
 [5,] "7"  "4"  "c" 
 [6,] "10" "7"  "d" 
 [7,] "8"  "6"  "e" 
 [8,] "1"  "2"  "a" 
 [9,] "6"  "5"  "b" 
[10,] "5"  "10" "b" 
> m[as.numeric(ind[,1]),ind[,3]]<-1
> m
      a b c d e f g h i j
 [1,] 1 1 1 1 1 0 0 0 0 1
 [2,] 1 1 1 1 1 0 0 0 0 1
 [3,] 1 1 1 1 1 0 0 0 0 1
 [4,] 1 1 1 1 1 0 0 0 0 1
 [5,] 1 1 1 1 1 0 0 0 0 1
 [6,] 1 1 1 1 1 0 0 0 0 1
 [7,] 1 1 1 1 1 0 0 0 0 1
 [8,] 1 1 1 1 1 0 0 0 0 1
 [9,] 1 1 1 1 1 0 0 0 0 1
[10,] 1 1 1 1 1 0 0 0 0 1

我期望a列具有3 1s（第4,2,8行），b列具有3 1s（9,6,5行），c列具有1 1（第7行），d列具有1 1（第10行），第e列為1 1（第8行），第j列為1 1（第3行）。

Answer 1

有一種方法可以對“ [”或“ [<-”使用兩列數字矩陣。 如果您想對列名和行名進行某種形式的查找，則可能（僅當您提供了適當的可重現示例時）。

> expTrans<-matrix(0, 3,4);expTrans
     [,1] [,2] [,3] [,4]
[1,]    0    0    0    0
[2,]    0    0    0    0
[3,]    0    0    0    0
> dmat <- matrix( c(1,3,4,2,2,2),ncol=3, byrow=TRUE);dmat
     [,1] [,2] [,3]
[1,]    1    3    4
[2,]    2    2    2
> colnames(expTrans)<- colnames(dmat); rownames(expTrans) <-rownames(dmat)
> expTrans[cbind(dmat[,2],dmat[,3] )] <- dmat[,1]
> expTrans
     [,1] [,2] [,3] [,4]
[1,]    0    0    0    0
[2,]    0    2    0    0
[3,]    0    0    0    1
> ?'['

修改后的問題的解決方案：

> m[cbind( as.numeric(ind[,1]), match( ind[,3], colnames(m) ) ) ] <- 1
> m
      a b c d e f g h i j
 [1,] 0 1 0 0 0 0 0 0 0 0
 [2,] 0 1 0 0 0 0 0 0 0 0
 [3,] 0 0 0 1 0 0 0 0 0 0
 [4,] 1 0 0 0 0 0 0 0 0 0
 [5,] 0 0 0 0 0 0 0 0 0 1
 [6,] 0 1 0 0 0 0 0 0 0 0
 [7,] 0 0 0 0 1 0 0 0 0 0
 [8,] 1 0 0 0 0 0 0 0 0 0
 [9,] 0 0 1 0 0 0 0 0 0 0
[10,] 1 0 0 0 0 0 0 0 0 0