R, accessing a column vector of a matrix by name

Question

In R I can access the data in a column vector of a column matrix by the following:

mat2[,1]

Each column of mat2 has a name. How can I retrieve the data from the first column by using the name attribute instead of [,1]?

For example suppose my first column had the name "saturn". I want something like

mat2[,1] == mat2[saturn]

Read the documentation, e.g. `?"["`, or any introduction to R. — Roland, Mar 08 '13 at 16:34

score 25 · Accepted Answer · answered Mar 08 '13 at 15:42

25

The following should do it:

mat2[,'saturn']

For example:

> x <- matrix(1:21, nrow=7, ncol=3)
> colnames(x) <- paste('name', 1:3)
> x[,'name 1']
[1] 1 2 3 4 5 6 7

answered Mar 08 '13 at 15:42

NPE

Thanks, I'm a beginner in R. also just to add that column name is case-sensitive. – Saqib Mustafa Abbasi Sep 18 '16 at 04:25
Just to add it can also be done like mat2$saturn – Saqib Mustafa Abbasi Sep 18 '16 at 14:38
@SaqibMustafaAbbasi in R, matrices are atomic, not recursive objects. If you try to use `$` on a matrix, you should get this error: https://stackoverflow.com/questions/23299684/r-error-in-xed-operator-is-invalid-for-atomic-vectors#23299802 – Dmitri May 26 '17 at 19:39

score 14 · Answer 2 · answered Mar 08 '13 at 15:53

Bonus information (adding to the first answer)

x[,c('name 1','name 2')]

would return two columns just as if you had done

x[,1:2]

And finally, the same operations can be used to subset rows

x[1:2,]

And if rows were named...

x[c('row 1','row 2'),]

Note the position of the comma within the brackets and with respect to the indices.

2 Answers2