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How to create a subset of a matrix in R using row names?
When we create a matrix in R, the row names and column names are not defined but we can define them separately. If we want to take a subset of rows of a matrix then row numbers can be used within single square brackets but if we want to do it with the names then we need to specify those names.
Example
M1<-matrix(1:25,ncol=5) rownames(M1)<-letters[1:5] M1
Output
[,1] [,2] [,3] [,4] [,5] a 1 6 11 16 21 b 2 7 12 17 22 c 3 8 13 18 23 d 4 9 14 19 25
Example
M1[c("a","b"),]Output
[,1] [,2] [,3] [,4] [,5] a 1 6 11 16 21 b 2 7 12 17 22
Example
M1[c("a","d"),]Output
[,1] [,2] [,3] [,4] [,5] a 1 6 11 16 21 d 4 9 14 19 24
Example
M1[c("a","e"),]Output
[,1] [,2] [,3] [,4] [,5] a 1 6 11 16 21 e 5 10 15 20 25
Example
M1[c("a","b","e"),]Output
[,1] [,2] [,3] [,4] [,5] a 1 6 11 16 21 b 2 7 12 17 22 e 5 10 15 20 25
Example
M1[c("a","b","d","e"),]Output
[,1] [,2] [,3] [,4] [,5] a 1 6 11 16 21 b 2 7 12 17 22 d 4 9 14 19 24 e 5 10 15 20 25
Example
M2<-matrix(1:100,nrow=10) rownames(M2)<-LETTERS[1:10] M2
Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] A 1 11 21 31 41 51 61 71 81 91 B 2 12 22 32 42 52 62 72 82 92 C 3 13 23 33 43 53 63 73 83 93 D 4 14 24 34 44 54 64 74 84 94 E 5 15 25 35 45 55 65 75 85 95 F 6 16 26 36 46 56 66 76 86 96 G 7 17 27 37 47 57 67 77 87 97 H 8 18 28 38 48 58 68 78 88 98 I 9 19 29 39 49 59 69 79 89 99 J 10 20 30 40 50 60 70 80 90 100
Example
M2[c("A","J"),]Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] A 1 11 21 31 41 51 61 71 81 91 J 10 20 30 40 50 60 70 80 90 100
Example
M2[c("A","D","F","I"),]Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] A 1 11 21 31 41 51 61 71 81 91 D 4 14 24 34 44 54 64 74 84 94 F 6 16 26 36 46 56 66 76 86 96 I 9 19 29 39 49 59 69 79 89 99
Example
M2[c("A","C","E","G","J"),]Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] A 1 11 21 31 41 51 61 71 81 91 C 3 13 23 33 43 53 63 73 83 93 E 5 15 25 35 45 55 65 75 85 95 G 7 17 27 37 47 57 67 77 87 97 J 10 20 30 40 50 60 70 80 90 100
Example
M3<-matrix(rnorm(25,1,0.04),nrow=5)
rownames(M3)<-c("Rate1","Rate2","Rate3","Rate4","Rate5")
M3Output
[,1] [,2] [,3] [,4] [,5] Rate1 1.0095550 0.9804156 0.9655588 1.025432 0.9420430 Rate2 0.9926681 0.9830571 0.9428085 1.000219 0.9980977 Rate3 1.0039020 1.0121637 1.0291146 1.062020 1.0822971 Rate4 1.0720653 1.0469583 0.9947673 1.065848 1.0165283 Rate5 0.9752784 1.0382877 0.9933063 1.011313 0.9942537
Example
M3["Rate3",]
Output
[1] 1.003902 1.012164 1.029115 1.062020 1.082297
Example
M3[c("Rate1","Rate5"),]Output
[,1] [,2] [,3] [,4] [,5] Rate1 1.0095550 0.9804156 0.9655588 1.025432 0.9420430 Rate5 0.9752784 1.0382877 0.9933063 1.011313 0.9942537
Example
M3[c("Rate1","Rate3","Rate5"),]Output
[,1] [,2] [,3] [,4] [,5] Rate1 1.0095550 0.9804156 0.9655588 1.025432 0.9420430 Rate3 1.0039020 1.0121637 1.0291146 1.062020 1.0822971 Rate5 0.9752784 1.0382877 0.9933063 1.011313 0.9942537
Updated on: 18-Oct-2020
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