On 2010-12-07 03:34, Andreas Borg wrote:
Hi all,I just stumbled across the difference between explicit and 'automatic' row names for data frames. Is there a quick way to find out if a data frame has automatic row names or not? Of course I know this for data frames that I create myself, but what if a function needs to extract this information for an argument? The following example shows that this property is not easily visible: > # data frame with automatic row names > df<- data.frame(a=1:2, b=3:4) > # data frame with explicit row names > df2<- data.frame(a=1:2, b=3:4, row.names=1:2) > # printing does not reveal any difference > df a b 1 1 3 2 2 4 > df2 a b 1 1 3 2 2 4 > # both are considered equal > all.equal(df, df2) [1] TRUE > identical(df, df2) [1] TRUE > # calling rownames gives the same result > rownames(df) [1] "1" "2" > rownames(df2) [1] "1" "2" > # when converting to a matrix, it makes a difference > as.matrix(df) a b [1,] 1 3 [2,] 2 4 > as.matrix(df2) a b 1 1 3 2 2 4 Thanks for any suggestion,
Check ?.row_names_info Peter Ehlers
Andreas
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