[R] inserting columns in the middle of a dataframe

[Prof Brian Ripley]

On Thu, 28 Sep 2006, Joe W. Byers wrote:

> Berton Gunter wrote:
>> Please folks -- use indexing.
>>
>> myframe<-myframe[,c(1,5,2,3,4)]
>>
>> Which begs the question: why bother rearranging the columns anyway, since
>> one can get them used, printed, etc. in any order you wish anytime you want
>> just by specifying the indices in the order you want them. I suspect the
>> question was motivated by too much Sas- or Excel -ism.

> Many of the time series classes expect a date in the first column of the
> matrix or data.frame when creating the date-time object.  Retrieving
> data in a SQL query from a dB returns a character representation of the
> date that requires conversion to a date.  Performing this conversion is
> easy but inserting this converted date column is not straight forward.

Well-written R <--> DBMS software does return a date or date-time, and if 
it is the first column retrieved by other software, you want to _replace_ 
the _first_ column, not really relevant to the topic of your subject line.
(Doing that is basic data manipulation, covered in Chapter 2 of MASS4, for 
example.)

The initial assertion is not (necessarily) true of "ts" or "irts" or "its" 
or "zoo", so quite a few time-series class generators expect a date or 
date-time to be specified separately.


>>> -----Original Message-----
>>> From: r-help-bounces at stat.math.ethz.ch
>>> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Timothy Bates
>>> Sent: Wednesday, September 13, 2006 3:05 PM
>>> To: Jon Minton; r-help at stat.math.ethz.ch
>>> Subject: Re: [R] inserting columns in the middle of a dataframe
>>>
>>>
>>>> Is there a built-in and simple way to insert new columns in
>>> a dataframe?
>>>
>>> You do this by collecting the columns in the new order you desire, and
>>> making a new frame.
>>>
>>> oldframe           <- data.frame(matrix(0:14,ncol=3))
>>> newcol              <- data.frame(20:24)
>>> names(newcol) <- "newcol"
>>> newframe         <- data.frame(c(oldframe[1],newcol, oldframe[2:3]))

-- 
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