[R] Problem with "merge" command duplicating values

[John Kane]

What package is 'grand.merge' in?

--- On Wed, 7/22/09, Archana Dayalu <dayalu.archana at gmail.com> wrote:

> From: Archana Dayalu <dayalu.archana at gmail.com>
> Subject: [R] Problem with "merge" command duplicating values
> To: r-help at r-project.org
> Received: Wednesday, July 22, 2009, 3:44 PM
> Hello,
> I am attempting to merge 8 different data sets into a
> "grand merge" data
> set; all their variable names are common except for the the
> gas measured.
> However, when I did a quick stat summary comparison of
> merged data with
> unmerged data, it turned out that R mysteriously duplicated
> thousands of
> values in the merged set and I have no idea why. I've not
> had this problem
> with merge in the past.... any thoughts?
> 
> To illustrate:
> 
> given the following objects (as data frames) with 1 unique
> and 10 common
> variables:
> h2_flasks
> co2c13_flasks
> co2o18_flasks
> ch4_flasks
> co2_flasks
> co_flasks
> n2o_flasks
> co2c14_flasks
> 
> #Merge objects into one data frame ("grand merge"):
> >obj.list <- ls(pattern='flasks')
> >grand.merge<-merge(get(obj.list[1]),get(obj.list[2]),all=TRUE)
> >for (ss in 3:length(obj.list)){
>    
> grand.merge<-merge(grand.merge,get(obj.list[ss]),all=TRUE)
>     }
> 
> #CH4 data extracted from grand merge
> >length(na.omit(grand.merge$CH4))
> [1] 29027
> 
> #Unmerged CH4 data only (from object ch4_flasks)
> > length(na.omit(ch4_flasks$CH4))
> [1] 23739
> 
> #So 5000+ CH4 values are mysteriously "added" to the grand
> merge file. This
> "duplicated value" problem occurs for all gas variables in
> the grand merged
> data, in varying degrees. (For example, H2 had only 2 extra
> values
> mysteriously added).
> 
> Thanks very much for any input.
> Archana
> 
>     [[alternative HTML version deleted]]
> 
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