[R] Header = T

peter dalgaard pdalgd at gmail.com
Wed Nov 23 11:38:07 CET 2011

On Nov 23, 2011, at 10:03 , Jim Lemon wrote:

> On 11/23/2011 06:47 AM, lucky7 wrote:
>> Hi,
>> I just start to use R today! I am reading the R Help on read.csv and the
>> description for header says "header is set to TRUE if and only if the first
>> row contains one fewer field than the number of columns". Why is that? My
>> data has the same number of fields in the first row as the number of
>> columns. I mean I have no problem opening my csv file I am just curious why
>> it should be one fewer.
> Hi lucky7,
> This looks like one of those little obscurities that sometimes appear in the help files. The default for read.csv is header=TRUE and I guess that the "...header is set to TRUE..." part means that if your file has one less field in the first line, header will be forced to TRUE as this is a part of the CSV specification. As Douglas Adams might have said,
> "Don't panic."

Actually, no. It's a "little obscurity" alright, but the root cause is that the help file was originally written for read.table, with read.csv and friends as later bolt-ons. These actually call read.table internally, but if the header argument is missing to read.csv, the default (TRUE) will be passed to read.table. Thus, there is no way to induce the first-line-shorter logic. No big deal; nobody writes CSV files following that convention anyway. 

The situation is in turn a niggle in the R language itself: missingness does not propagate. 

> Jim
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Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

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