[R] Multiple cbind according to filename

[Uwe Ligges]

On 25.05.2012 16:42, Ken wrote:
> Matthew Ouellette<mouellette89<at>  gmail.com>  writes:
>
>>
>> Hi all,
>>
>> I'm just a beginner with R but I have not been able to search for any
>> relevant answer to my problem.  I apologize if it has in fact been asked
>> before.
>>
>> Recently I've realized that I need to combine hundreds of pairs of data
>> frames.  The filenames of the frames I need to combine have unique strings.
>>   This is my best guess as to the approach to take:
>>
>>   filenames<-list.files()
>>
>> filenames
>> [1] "a1.csv" "a2.csv" "b1.csv" "b2.csv" "c1.csv" "c2.csv"
>>
>> alldata<-lapply(filenames, read.csv, header=TRUE)
>>
>>   names(alldata)<-filenames
>>   summary(alldata)
>>         Length Class      Mode
>> a1.csv 27     data.frame list
>> a2.csv 27     data.frame list
>> b1.csv 27     data.frame list
>> b2.csv 27     data.frame list
>> c1.csv 27     data.frame list
>> c2.csv 27     data.frame list
>>
>> My next step would be to cbind files that share a common string at the
>> beginning, such as:
>> cbind(alldata[[1]],alldata[[2]])
>> cbind(alldata[[3]],alldata[[4]])
>> cbind(alldata[[5]],alldata[[6]])
>> ...



I think the actual question is how to cbind() all data.frames. The 
answer for that is:

result <- do.call(cbind, alldata)

Best,
Uwe Ligges



>> but file list is hundreds of files long (but is sorted alphanumerically
>> such as in this example - not sure if this is relevant).  If I had to
>> guess, I'd do something like this:
>>
>> which(names(alldata)==...), to identify which elements to combine based on
>> unique filename
>>
>> OR
>> x<-seq(1,length(alldata), 2)
>> y=x+1
>> z<-cbind(x,y)
>> z
>>       x y
>> [1,] 1 2
>> [2,] 3 4
>> [3,] 5 6
>>
>> to use the frame created in z to combine based on rows,
>>
>> then use a looped cbind function (or *apply function with nested cbind
>> function?) using the previously returned indexes to create my new combined
>> data frames, including a step to write the frames to a new unique filename
>> (not sure how to do that step in this context).  These last steps I've
>> tried a lot of code but nothing worth mentioning as it has all failed
>> miserably.
>>
>> I appreciate the help,
>>
>> M
>>
>> 	[[alternative HTML version deleted]]
>>
>>
>
> Hi Matthew,
>
> You could try using substr() if the cbind is based on a common string in the
> file name just makes sure that the strings in filenames is in the same order as
> the files are in list.files:
>
> a1<- data.frame("col1" = seq(1,10, 1))
> a2<- data.frame("col2" = seq(11,20, 1))
> b1<- data.frame("col3" = seq(21,30, 1))
> b2<- data.frame("col4" = seq(31,40, 1))
>
> filenames<- c("a1", "a2", "b1", "b2")
>
> list.files<- list(a1, a2, b1, b2)
> first.letter<- substr(filenames, 1,1)
> unique.first.letter<- unique(first.letter)
>
> l.files<- list()
> for(i in 1:length(unique.first.letter)){
>    l.files[[i]] = as.data.frame(list.files[first.letter == unique.first.letter[i]])
> }
>
>
> HTH,
> Ken
>
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