[R] Exporting columns into multiple files - loop query

[David Winsemius]

On Mar 25, 2011, at 10:45 PM, WOOD, Matthew wrote:

> Hi,
>
> I'm using a loop to extract 2 columns from an array into multiple  
> files.
> I can use the following to export 3 files, containing column 'ID'  
> with one of
> the three event columns.
>
>> ID<-c("A","B","C","D","E","F")
>> event1<-c(0,1,0,0,1,0)
>> event2<-c(1,1,0,1,0,0)
>> event3<-c(1,0,1,0,1,0)
>> data<-cbind(ID,event1,event2,event3)
>> data
>     ID  event1 event2 event3
> [1,] "A" "0"    "1"    "1"
> [2,] "B" "1"    "1"    "0"
> [3,] "C" "0"    "0"    "1"
> [4,] "D" "0"    "1"    "0"
> [5,] "E" "1"    "0"    "1"
> [6,] "F" "0"    "0"    "0"
>
> The data represent individuals that are either seen (1) or not seen  
> (0) on
> several occasions.
>>
>> n<-ncol(data)
>>
>> for(i in 2:n) {
> + df<-data.frame(data[,i],ID)
> + myfile<-gsub("( )", "",paste(i,".txt")) # name file by year
> + write.table(df, file=myfile,
> sep="\t",row.names=F,col.names=F,quote=FALSE,append=FALSE)
> + }
>
> My question: How can I add a function to this loop, to delete rows  
> in the
> data frame in which the event is equal to zero?
>

Since the expression data[,i] is returning a vector,you could just use  
its values to filter both the "data" and the "ID" vectors:

for(i in 2:n) {
  df<-data.frame( data[,i][data[,i]!=0], ID[data[,i]!=0] )
  myfile<-gsub("( )", "",paste(i,".txt")) # name file by year
  write.table(df, file=myfile,
sep="\t",row.names=F,col.names=F,quote=FALSE,append=FALSE)
  }


Or you could filter just the data.frame with "[":

for(i in 2:n) {
  df<-data.frame(data[,i],ID)[ data[,i]!=0, ]
  myfile<-gsub("( )", "",paste(i,".txt")) # name file by year
  write.table(df, file=myfile,
sep="\t",row.names=F,col.names=F,quote=FALSE,append=FALSE)
  }

There are probably more elegant ways but you do now have method that  
"work".

-- 
David.

> An desired file output would be:
>     ID  event2
> [1,] "A" "1"
> [2,] "B" "1"
> [3,] "D" "1"
>
> I can handle this taking each file separately using subscripts, but my
> attempts to amend the loop, and be able to run this code on a bunch  
> of large
> mutliple event files, have failed.
>
> With grateful thanks in advance,
>
> Matt
>
> --
> Matt Wood
> Department of Natural and Social Sciences
> University of Gloucestershire
> Francis Close Hall
> Cheltenham
> GL50 4AZ
>
>
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David Winsemius, MD
West Hartford, CT