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How to filter single column of a matrix with column name in R?
To filter a single column of a matrix in R if the matrix has column names, we can simply use single square brackets but this will result in a vector without the column name. If we want to use the column name then column name or column number needs to be passed with drop=FALSE argument as shown in the below examples.
Example1
> M1<-matrix(sample(0:1,80,replace=TRUE),ncol=4)
> colnames(M1)<-c("V1","V2","V3","V4")
> M1Output
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
Extracting column V1 from M1 −
> M1[,"V1",drop = FALSE]
Output
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
Example2
> M2<-matrix(sample(c("Yes","No"),40,replace = TRUE),ncol=2)
> colnames(M2)<-c("Binary1","Binary2")
> M2Output
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"
Extracting column Binary2 from M2 −
> M2[,"Binary2",drop = FALSE]
Output
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"
Updated on: 04-Mar-2021
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