# 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