[R] Why do I have a column called row.names?

[Ed Siefker]

I did read that, and I still don't understand why I have a column
called row.names.
I used "row.names = NULL" in order to get numbered row names, which was
successful:

> row.names(BACS)
[1] "1" "2" "3" "4"

I don't see what this has to do with an extraneous column name.  Can you be
more explicit as to what exactly I'm supposed to take away from this segment
of the help file?  Thanks.

On Mon, Jun 4, 2012 at 1:05 PM, David L Carlson <dcarlson at tamu.edu> wrote:
> Try help("read.delim") - always a good strategy before using a function for
> the first time:
>
> In it, you will find: "Using row.names = NULL forces row numbering. Missing
> or NULL row.names generate row names that are considered to be 'automatic'
> (and not preserved by as.matrix)."
>
> ----------------------------------------------
> David L Carlson
> Associate Professor of Anthropology
> Texas A&M University
> College Station, TX 77843-4352
>
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> project.org] On Behalf Of Ed Siefker
>> Sent: Monday, June 04, 2012 12:47 PM
>> To: r-help at r-project.org
>> Subject: [R] Why do I have a column called row.names?
>>
>> I'm trying to read in a tab separated table with read.delim().
>> I don't particularly care what the row names are.
>> My data file looks like this:
>>
>>
>> start   stop    Symbol  Insert sequence Clone End Pair  FISH
>> 203048  67173930        ABC8-43024000D23                TI:993812543
>>  TI:993834585
>> 255176  87869359        ABC8-43034700N15                TI:995224581
>>  TI:995237913
>> 1022033 1060472 ABC27-1253C21           TI:2094436044   TI:2094696079
>> 1022033 1061172 ABC23-1388A1            TI:2120730727   TI:2121592459
>>
>>
>>
>> I have to do something with row.names because my first column has
>> duplicate entries.  So I read in the file like this:
>>
>> > BACS<-read.delim("testdata.txt", row.names=NULL, fill=TRUE)
>> > head(BACS)
>>   row.names    start             stop Symbol Insert.sequence
>> Clone.End.Pair
>> 1    203048 67173930 ABC8-43024000D23     NA    TI:993812543
>> TI:993834585
>> 2    255176 87869359 ABC8-43034700N15     NA    TI:995224581
>> TI:995237913
>> 3   1022033  1060472    ABC27-1253C21     NA   TI:2094436044
>> TI:2094696079
>> 4   1022033  1061172     ABC23-1388A1     NA   TI:2120730727
>> TI:2121592459
>>   FISH
>> 1   NA
>> 2   NA
>> 3   NA
>> 4   NA
>>
>>
>> Why is there a column named "row.names"?  I've tried a few different
>> ways of invoking this, but I always get the first column named
>> row.names,
>> and the rest of the columns shifted by one.
>>
>> Obviously I could fix this by using row.names<-, but I'd like to
>> understand
>> why this happens.  Any insight?
>>
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>