row.names are dropped when extracting one column ?

On Tue, 2004-03-02 at 11:59, ryszard.czerminski at pharma.novartis.com
wrote:

Apparently row names are dropped when I extract
single column from a data frame. Why this behaviour ?

y <- as.matrix(df[,1:2]); length(row.names(y))

[1] 324

y <- as.matrix(df[,1:1]); length(row.names(y))

[1] 0

Best regards,

Ryszard

Please see R-FAQ 7.7:

"Why do my matrices lose dimensions?"

HTH,

Marc Schwartz

Apparently row names are dropped when I extract
single column from a data frame. Why this behaviour ?

y <- as.matrix(df[,1:2]); length(row.names(y))

[1] 324

y <- as.matrix(df[,1:1]); length(row.names(y))

[1] 0

Why are you converting a subsetted data frame to a matrix?  df[, 1:2] is a 
data frame, and df[, 1:1] is a single column (most likely a vector). The 
latter is not going to have row names, but it might have names.  It 
happens that in S the row names are not copied across as names.

row.names applies to a data frame, and not to a matrix, strictly.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595