[R] appending and merging data frames

Thu Feb 7 18:59:01 CET 2013

I gave a small number of examples in my first email.

For append, in Stata any variable that is missing in the 
other dataset is automatically inserted with all values set
to the missing value. In R, one would first have to compare
the columns in both data frames and generate columns
apropriately. 

For merge, when merging dataset A with dataset B on some 
set of key variables, it is possible to specify if the
join should be done 1:1, 1:n, n:1 or n:m. Stata creates
a data structure that contains information about which 
observations could or could not be matched and which 
matches did not fit the 1:1/1:n or n:1 join pattern.

Again, I know that in R it is not hard to program all that
yourself (while programming in Stata is something different 
altogether), 
I just wondered if for these operations, which probably
are needed quite often, there are some additional packages 
or existing code that already deals with most of the situations
one encounters when appending/merging.

The background is that I am making the move from other stats
packages (including Stata) to R myself and I also want to 
motivate others to do it.

Also, before I go about implementing my own utility functions
for this, I wanted to make sure that something much better
isn't already out there (it usually is, especially when one
is a beginner).

> -----Original Message-----
> From: dwinsemius at comcast.net
> Sent: Thu, 7 Feb 2013 09:46:02 -0800
> To: johsmi9933 at inbox.com
> Subject: Re: [R] appending and merging data frames
> 
> 
> On Feb 7, 2013, at 9:12 AM, John Smith wrote:
> 
>> Hi Gerrit,
>> 
>> as I said in my original email, I already know both the
>> merge and the rbind commands, but I think that many
>> standard situations (I have given just a few) require
>> rather clumsy ad-hoc programming. So I was wondering
>> if there are any packages or existing code that would
>> make it easier to handle the diverse append/merge
>> tasks that tend to occur rather frequently.
>> For at least some of these tasks, other stats
>> packages, like Stata do provide out-of-the box
>> commands or command options.
>> Again, I just want to know if there is already some
>> package or code for this out there somewhere, especially
>> for appending tasks (automatically taking care of
>> missing variables, renaming, data types etc.)
>> The RSiteSearch() function is helpful and came up
>> with slightly different versions of merge but nothing
>> for append.
> 
> The sqldf package provides an interface to popular database drivers. I
> do not think your question provides enough specificity to go much
> further. You say Stata provides ... something... but you do not really
> explain what that something is. My efforts to understand the Stata
> documentation for the egen command left me shaking my head in
> disbelief at its opacity, and caused me to appreciate further the
> efforts of the R developers to make our help system available. The
> most productive approach would be to present a simple example in R code.
> 
> --
> David.
> 
>> 
>> John
>> 
>>> -----Original Message-----
>>> From: gerrit.eichner at math.uni-giessen.de
>>> Sent: Thu, 7 Feb 2013 16:57:13 +0100 (MET)
>>> To: johsmi9933 at inbox.com
>>> Subject: Re: [R] appending and merging data frames
>>> 
>>> Hello, John,
>>> 
>>> as a start take a look at
>>> 
>>> ?merge
>>> 
>>> And to (maybe) get a bit overwhelmed at first sight use
>>> 
>>> RSiteSearch( "merge")
>>> 
>>> 
>>>  Hth  --  Gerrit
>>> 
>>> On Thu, 7 Feb 2013, John Smith wrote:
>>> 
>>>> I know that the basic approach to append or merge data frames is
>>>> using
>>>> the rbind and merge commands.
>>>> However, if I understand things correctly, for both commands one
>>>> needs
>>>> to do quite some additional programming to get e.g. behavior as
>>>> with the
>>>> Stata append and morge commands or to achieve some things which I
>>>> think
>>>> users need quite frequently.
>>>> 
>>>> E.g. for appending, the data frame must have identical column
>>>> names. In
>>>> order to rename columns or in order to add columns with missing
>>>> values
>>>> if necessary, additional programming is needed.
>>>> For merging, all matches get combined, so it is not easily
>>>> possible to
>>>> check for 1:1 or 1:n matches or limit the join to such kind of
>>>> matches,
>>>> is it?
>>>> Those are just examples, there are a number of additional details
>>>> that
>>>> would be useful to be able to control for merging/appending (maybe
>>>> at
>>>> the expense of restricting the operation to just data frames).
>>>> 
>>>> So my question is: are there any packages or existing utility
>>>> functions
>>>> which would provide append and merge functionality at a slightly
>>>> higher
>>>> (user-friendly) level?
>>>> 
>>>> Although I am quite a noob, I would be prepared to give it a try and
>>>> program these myself, but I have the feeling that this must be so
>>>> common
>>>> that maybe it would mean re-inventing the wheel?
>>>> 
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>>>> PLEASE do read the posting guide
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>> 
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>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> 
> David Winsemius, MD
> Alameda, CA, USA
>

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