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How to select a column of a matrix by column name in R?
When we create a matrix in R, its column names are not defined but we can name them or might import a matrix that might have column names. If the column names are not defined then we simply use column numbers to extract the columns but if we have column names then we can select the column by name as well as its name.
Example1
M1 <-matrix(1:25,nrow=5) M1
Output
[,1] [,2] [,3] [,4] [,5] [1,] 1 6 11 16 21 [2,] 2 7 12 17 22 [3,] 3 8 13 18 23 [4,] 4 9 14 19 24 [5,] 5 10 15 20 25
Example
colnames(M1) <-c("C1","C2","C3","C4","C5") M1
Output
C1 C2 C3 C4 C5 [1,] 1 6 11 16 21 [2,] 2 7 12 17 22 [3,] 3 8 13 18 23 [4,] 4 9 14 19 24 [5,] 5 10 15 20 25
Example
M1[,"C1"]
Output
[1] 1 2 3 4 5
Example
M1[,"C2"]
Output
[1] 6 7 8 9 10
Example
M1[,"C4"]
[1] 16 17 18 19 20
Example
M1[,"C5"]
Output
[1] 21 22 23 24 25
Example2
M2 <-matrix(sample(1:100,36),nrow=6) M2
Output
[,1] [,2] [,3] [,4] [,5] [,6] [1,] 97 53 27 60 13 8 [2,] 41 98 38 73 74 57 [3,] 65 54 15 49 9 5 [4,] 46 87 100 19 94 62 [5,] 6 23 91 45 34 32 [6,] 71 51 26 85 29
Example
colnames(M2) <-c("Rate","Percentage","Class","Group","ID","Section") M2
Output
Rate Percentage Class Group ID Section [1,] 97 53 27 60 13 8 [2,] 41 98 38 73 74 57 [3,] 65 54 15 49 9 5 [4,] 46 87 100 19 94 62 [5,] 6 23 91 45 34 32 [6,] 71 51 26 85 29 70
Example
M2[,"Rate"]
Output
[1] 97 41 65 46 6 71
Example
M2[,"Percentage"]
Output
[1] 53 98 54 87 23 51
Example
M2[,"Class"]
Output
[1] 27 38 15 100 91 26
Example
M2[,"Group"]
Output
[1] 60 73 49 19 45 85
Example
M2[,"ID"]
Output
[1] 13 74 9 94 34 29
Example
M2[,"Section"]
Output
[1] 8 57 5 62 32 70
Example3
M3 <-matrix(1:100,nrow=10) colnames(M3) <-c("Var1","Var2","Var3","Var4","Var5","Var6","Var7","Var8","Var9","Var10") M3
Output
Var1 Var2 Var3 Var4 Var5 Var6 Var7 Var8 Var9 Var10 [1,] 1 11 21 31 41 51 61 71 81 91 [2,] 2 12 22 32 42 52 62 72 82 92 [3,] 3 13 23 33 43 53 63 73 83 93 [4,] 4 14 24 34 44 54 64 74 84 94 [5,] 5 15 25 35 45 55 65 75 85 95 [6,] 6 16 26 36 46 56 66 76 86 96 [7,] 7 17 27 37 47 57 67 77 87 97 [8,] 8 18 28 38 48 58 68 78 88 98 [9,] 9 19 29 39 49 59 69 79 89 99 [10,] 10 20 30 40 50 60 70 80 90 100
Example
M3[,"Var1"]
Output
[1] 1 2 3 4 5 6 7 8 9 10
Example
M3[,"Var5"]
Output
[1] 41 42 43 44 45 46 47 48 49 50
Example
M3[,"Var7"]
Output
[1] 61 62 63 64 65 66 67 68 69 70
Example
M3[,"Var9"]
Output
[1] 81 82 83 84 85 86 87 88 89 90
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