Row names column names in R

Question

Do the following function pairs generate exactly the same results   Pair 1  names    amp  colnames      Pair 2  rownames    amp  row names

User · Accepted Answer

As Oscar Wilde said

Consistency is the last refuge of the unimaginative.

R is more of an evolved rather than designed language, so these things happen. names() and colnames() work on a data.frame but names() does not work on a matrix:

R> DF <- data.frame(foo=1:3, bar=LETTERS[1:3])
R> names(DF)
[1] "foo" "bar"
R> colnames(DF)
[1] "foo" "bar"
R> M <- matrix(1:9, ncol=3, dimnames=list(1:3, c("alpha","beta","gamma")))
R> names(M)
NULL
R> colnames(M)
[1] "alpha" "beta"  "gamma"
R>

User · Answer

Just to expand a little on Dirk s example   It helps to think of a data frame as a list with equal length vectors   That s probably why names works with a data frame but not a matrix   The other useful function is dimnames which returns the names for every dimension   You will notice that the rownames function actually just returns the first element from dimnames   Regarding rownames and row names  I can t tell the difference  although rownames uses dimnames while row names was written outside of R   They both also seem to work with higher dimensional arrays    gt a  lt - array 1 5  1 4   gt  a 1      gt  rownames a   lt -  a   gt  row names a   1   a   gt  a     1  1         1    2  a    1    2   gt  dimnames a    1    1   a     2   NULL    3   NULL    4   NULL

User · Answer

I think that using colnames and rownames makes the most sense  here s why   Using names has several disadvantages   You have to remember that it means  column names   and it only works with data frame  so you ll need to call colnames whenever you use matrices  By calling colnames  you only have to remember one function   Finally  if you look at the code for colnames  you will see that it calls names in the case of a data frame anyway  so the output is identical   rownames and row names return the same values for data frame and matrices  the only difference that I have spotted is that where there aren t any names  rownames will print  NULL   as does colnames   but row names returns it invisibly   Since there isn t much to choose between the two functions  rownames wins on the grounds of aesthetics  since it pairs more prettily withcolnames    Also  for the lazy programmer  you save a character of typing

User · Answer

And another expansion     create dummy matrix set seed 10  m  lt - matrix round runif 25  1  5    5  d  lt - as data frame m    If you want to assign new column names you can do following on data frame     an identical effect can be achieved with colnames      names d   lt - LETTERS 1 5   gt  d   A B C D E 1 3 2 4 3 4 2 2 2 3 1 3 3 3 2 1 2 4 4 4 3 3 3 2 5 1 3 2 4 3   If you  however run previous command on matrix  you ll mess things up   names m   lt - LETTERS 1 5   gt  m        1    2    3    4    5   1      3    2    4    3    4  2      2    2    3    1    3  3      3    2    1    2    4  4      4    3    3    3    2  5      1    3    2    4    3 attr   names     1   A   B   C   D   E  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA   20  NA  NA  NA  NA  NA  NA    Since matrix can be regarded as two-dimensional vector  you ll assign names only to first five values  you don t want to do that  do you    In this case  you should stick with colnames     So there

[r] Row names & column names in R

Examples related to r

Examples related to columnname

Examples related to rowname