[R] Multiple merge, better solution?

baptiste auguie ba208 at exeter.ac.uk
Thu Feb 19 12:43:06 CET 2009


If you don't mind I've added this example to the R wiki,

http://wiki.r-project.org/rwiki/doku.php?id=tips:data-frames:merge

It would be very nice if a R guru could check that the information I  
put is not complete fantasy. Feel free to remove as appropriate.

Best wishes,

baptiste


On 19 Feb 2009, at 11:00, Lauri Nikkinen wrote:

> Thanks, both solutions work fine. I tried these solutions to my real
> data, and I got an error
>
> Error in match.names(clabs, names(xi)) :
>  names do not match previous names
>
> I refined this example data to look more like my real data, this also
> produces the same error. Any ideas how to prevent this error?
>
> DF1 <- data.frame(var1 = letters[1:5], a = rnorm(5), b = rnorm(5), c  
> = rnorm(5))
> DF2 <- data.frame(var1 = letters[3:7], a = rnorm(5), b = rnorm(5), c  
> = rnorm(5))
> DF3 <- data.frame(var1 = letters[6:10], a = rnorm(5), b = rnorm(5), c
> = rnorm(5))
> DF4 <- data.frame(var1 = letters[8:12], a = rnorm(5), b = rnorm(5), c
> = rnorm(5))
>
>> g <- merge(DF1, DF2, by.x="var1", by.y="var1", all=T)
>> g <- merge(g, DF3, by.x="var1", by.y="var1", all=T)
>> merge(g, DF4, by.x="var1", by.y="var1", all=T)
>
> Error in match.names(clabs, names(xi)) :
>  names do not match previous names
>
>> DF <- DF1
>> for ( .df in list(DF2,DF3,DF4) ) {
> +  DF <-merge(DF,.df,by.x="var1", by.y="var1", all=T)
> + }
>
> Error in match.names(clabs, names(xi)) :
>  names do not match previous names
>
>> Reduce(function(x, y) merge(x, y, all=T,by.x="var1", by.y="var1"),  
>> list(DF1, DF2, DF3, DF4), accumulate=F)
>
> Error in match.names(clabs, names(xi)) :
>  names do not match previous names
>
> - Lauri
>
> 2009/2/19 baptiste auguie <ba208 at exeter.ac.uk>:
>> Hi,
>>
>>
>> I think Reduce could help you.
>>
>> DF1 <- data.frame(var1 = letters[1:5], a = rnorm(5))
>> DF2 <- data.frame(var1 = letters[3:7], b = rnorm(5))
>> DF3 <- data.frame(var1 = letters[6:10], c = rnorm(5))
>> DF4 <- data.frame(var1 = letters[8:12], d = rnorm(5))
>>
>> g <- merge(DF1, DF2, by.x="var1", by.y="var1", all=T)
>> g <- merge(g, DF3, by.x="var1", by.y="var1", all=T)
>> g <- merge(g, DF4, by.x="var1", by.y="var1", all=T)
>>
>> test <- Reduce(function(x, y) merge(x, y, all=T,by.x="var1",  
>> by.y="var1"),
>>                       list(DF1, DF2, DF3, DF4), accumulate=F)
>>
>> all.equal(test, g) # TRUE
>>
>>
>> As a warning, it's the first time I've ever used it myself...
>>
>>
>> Hope this helps,
>>
>> baptiste
>>
>>
>>
>> On 19 Feb 2009, at 10:21, Lauri Nikkinen wrote:
>>
>>> Hello,
>>>
>>> My problem is that I would like to merge multiple files with a  
>>> common
>>> column but merge accepts only two
>>> data.frames to merge. In the real situation, I have 26 different
>>> data.frames with a common column. I can of course use merge many  
>>> times
>>> (see below) but what would be more sophisticated solution? For loop?
>>> Any ideas?
>>>
>>> DF1 <- data.frame(var1 = letters[1:5], a = rnorm(5))
>>> DF2 <- data.frame(var1 = letters[3:7], b = rnorm(5))
>>> DF3 <- data.frame(var1 = letters[6:10], c = rnorm(5))
>>> DF4 <- data.frame(var1 = letters[8:12], d = rnorm(5))
>>>
>>> g <- merge(DF1, DF2, by.x="var1", by.y="var1", all=T)
>>> g <- merge(g, DF3, by.x="var1", by.y="var1", all=T)
>>> merge(g, DF4, by.x="var1", by.y="var1", all=T)
>>>
>>> Thanks in advance.
>>>
>>> -Lauri
>>>
>>> ______________________________________________
>>> 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.
>>
>> _____________________________
>>
>> Baptiste Auguié
>>
>> School of Physics
>> University of Exeter
>> Stocker Road,
>> Exeter, Devon,
>> EX4 4QL, UK
>>
>> Phone: +44 1392 264187
>>
>> http://newton.ex.ac.uk/research/emag
>> ______________________________
>>
>>

_____________________________

Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag



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