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

 Live Demo

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

 Live Demo

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

 Live Demo

M3<-matrix(rnorm(25,1,0.04),nrow=5)
rownames(M3)<-c("Rate1","Rate2","Rate3","Rate4","Rate5")
M3

Output

[,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