如何在R中使用列名过滤矩阵的单列？
如果矩阵有列名，要在 R 中过滤矩阵的单个列，我们可以简单地使用单个方括号，但这将导致没有列名的向量。如果我们想使用列名，则需要使用 drop=FALSE 参数传递列名或列号，如下面的示例所示。
示例 1
> M1<-matrix(sample(0:1,80,replace=TRUE),ncol=4)输出结果> colnames(M1)<-c("V1","V2","V3","V4")
> M1
V1 V2 V3 V4[1,] 0 0 1 0
[2,] 1 1 1 1
[3,] 0 0 0 0
[4,] 0 1 1 0
[5,] 1 1 1 1
[6,] 0 1 1 0
[7,] 0 1 0 1
[8,] 1 1 0 1
[9,] 1 1 0 1
[10,] 0 0 1 0
[11,] 0 0 0 1
[12,] 0 1 0 0
[13,] 0 0 0 0
[14,] 1 0 0 0
[15,] 0 1 0 1
[16,] 0 0 1 0
[17,] 1 1 1 1
[18,] 1 0 1 1
[19,] 1 0 1 1
[20,] 0 0 0 0
从 M1 中提取列 V1 -
> M1[,"V1",drop = FALSE]输出结果
V1[1,] 0
[2,] 1
[3,] 0
[4,] 0
[5,] 1
[6,] 0
[7,] 0
[8,] 1
[9,] 1
[10,] 0
[11,] 0
[12,] 0
[13,] 0
[14,] 1
[15,] 0
[16,] 0
[17,] 1
[18,] 1
[19,] 1
[20,] 0
例2
> M2<-matrix(sample(c("Yes","No"),40,replace = TRUE),ncol=2)> colnames(M2)<-c("Binary1","Binary2")
> M2
输出结果Binary1 Binary2[1,] "Yes" "Yes"
[2,] "Yes" "No"
[3,] "Yes" "No"
[4,] "Yes" "Yes"
[5,] "Yes" "Yes"
[6,] "No" "No"
[7,] "Yes" "Yes"
[8,] "No" "Yes"
[9,] "No" "No"
[10,] "Yes" "Yes"
[11,] "Yes" "Yes"
[12,] "Yes" "No"
[13,] "Yes" "No"
[14,] "No" "Yes"
[15,] "No" "Yes"
[16,] "Yes" "Yes"
[17,] "No" "Yes"
[18,] "Yes" "Yes"
[19,] "Yes" "Yes"
[20,] "No" "No"
从 M2 中提取列 Binary2 -
> M2[,"Binary2",drop = FALSE]输出结果
Binary2[1,] "Yes"
[2,] "No"
[3,] "No"
[4,] "Yes"
[5,] "Yes"
[6,] "No"
[7,] "Yes"
[8,] "Yes"
[9,] "No"
[10,] "Yes"
[11,] "Yes"
[12,] "No"
[13,] "No"
[14,] "Yes"
[15,] "Yes"
[16,] "Yes"
[17,] "Yes"
[18,] "Yes"
[19,] "Yes"
[20,] "No"
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