[R] Merging data frames one of which is NULL

[Dimitri Liakhovitski]

Thanks a lot, Joshua.
You might be right.
I am thinking of creating a list (as a placeholder) and then merging
the elements of the list.
Dimitri

On Tue, Nov 9, 2010 at 12:11 PM, Joshua Wiley <jwiley.psych at gmail.com> wrote:
> Hi Dimitri,
>
> I have some doubts whether storing the results of a loop in a data
> frame and merging it with every run is the most efficient way of doing
> things, but I do not know your situation.  This does what you want, I
> believe, but I suspect it could be quite slow.  I worked around the
> placeholder issue using an if statement.
>
> HTH,
>
> Josh
>
> for (i in 1:10) {
>  x <- data.frame(a = 1, b = 2, c = i)
>  if (i == 1) {
>    y <- x
>  } else {
>    y <- merge(x, y, all.x = TRUE, all.y = TRUE)
>  }
> }
>
> On Tue, Nov 9, 2010 at 8:42 AM, Dimitri Liakhovitski
> <dimitri.liakhovitski at gmail.com> wrote:
>> Hello!
>>
>> I am running a loop. The result of each run of the loop is a data
>> frame. I am merging all the data frames.
>> For exampe:
>>
>> The dataframe from run 1:
>> x<-data.frame(a=1,b=2,c=3)
>>
>> The dataframe from run 2:
>> y<-data.frame(a=10,b=20,d=30)
>>
>> What I want to get is:
>> merge(x,y,all.x=T,all.y=T)
>>
>> Then I want to merge it with the output of the 3rd run, etc.
>>
>> Unfortunately, I can't create the placeholder for the overall resutls
>> BEFORE I run the loop because I don't even know how many columns I'll
>> end up with - after merging all the data frames.
>> I was thinking of creating an empty list:
>>
>> first<-NULL
>>
>> ...and then updating it during each run by merging it with the data
>> frame that is the output of the run. However, when I try to merge the
>> empty list with any non-empty data frame - it ends up empty:
>> merge(first,a,,all.x=T,all.y=T)
>>
>> Is there a way to make it merge while keeping everything?
>> Thanks a lot!
>> --
>> Dimitri Liakhovitski
>> Ninah Consulting
>> www.ninah.com
>>
>> ______________________________________________
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
>
> --
> Joshua Wiley
> Ph.D. Student, Health Psychology
> University of California, Los Angeles
> http://www.joshuawiley.com/
>



-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com