R help - Dec 2010 - How to find out if a data frame has automatic row names?

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,

Andreas

-- 
Andreas Borg
Medizinische Informatik

UNIVERSIT?TSMEDIZIN
der Johannes Gutenberg-Universit?t
Institut f?r Medizinische Biometrie, Epidemiologie und Informatik
Obere Zahlbacher Stra?e 69, 55131 Mainz
www.imbei.uni-mainz.de

Telefon +49 (0) 6131 175062
E-Mail: borg at imbei.uni-mainz.de

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If as.matrix distinguishes between the two options, then you could look
at the code for that function and see how it's done.

Sarah

On Tue, Dec 7, 2010 at 6:34 AM, Andreas Borg
<andreas.borg at unimedizin-mainz.de> 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,
>
> Andreas
>
> --
> Andreas Borg
> Medizinische Informatik
>
-- 
Sarah Goslee\
http://www.functionaldiversity.org

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
>

That does it. Thanks!
>
> Check ?.row_names_info
>
> Peter Ehlers
>
>> Andreas
>>
>
>

-- 
Andreas Borg
Medizinische Informatik

UNIVERSIT?TSMEDIZIN
der Johannes Gutenberg-Universit?t
Institut f?r Medizinische Biometrie, Epidemiologie und Informatik
Obere Zahlbacher Stra?e 69, 55131 Mainz
www.imbei.uni-mainz.de

Telefon +49 (0) 6131 175062
E-Mail: borg at imbei.uni-mainz.de

Diese E-Mail enth?lt vertrauliche und/oder rechtlich gesch?tzte Informationen.
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