[R] Long to wide format without time variable

[Alan Cohen]

Hi all,

I am trying to convert a data set of physician death codings (each individual's cause of death is coded by multiple physicians) from long to wide format, but the "reshape" function doesn't seem to work because it requires a "time" variable to identify the sequence among the repeated observations within individuals.  My data set has no order, and different numbers of physicians code each death, up to 23.  It is also quite large, so for-loops are very slow, and I'll need to repeat the procedure multiple times.  So I'm looking for a processor-efficient way to replicate "reshape" without a time variable.

Thanks in advance for any help you can provide.  A worked example and some code I've tried are below.  I'm working with R v2.8.1 on Windows XP Professional.

Cheers,
Alan Cohen

Here's what my data look like now:

> id <- rep(1:5,2)
> COD <- c("A01","A02","A03","A04","A05","B01","A02","B03","B04","A05")
> MDid <- c(1:6,3,5,7,2)
> data <- as.data.frame(cbind(id,COD,MDid))
> data
   id COD MDid
1   1 A01    1
2   2 A02    2
3   3 A03    3
4   4 A04    4
5   5 A05    5
6   1 B01    6
7   2 A02    3
8   3 B03    5
9   4 B04    7
10  5 A05    2

And here's what I'd like them to look like:

> id2 <- 1:5
> COD.1 <- c("A01","A02","A03","A04","A05")
> COD.2 <- c("B01","A02","B03","B04","A05")
> MDid.1 <- 1:5
> MDid.2 <-c(6,3,5,7,2)
> data.wide <- as.data.frame(cbind(id2,COD.1,COD.2,MDid.1,MDid.2))
> data.wide
  id2 COD.1 COD.2 MDid.1 MDid.2
1   1   A01   B01      1      6
2   2   A02   A02      2      3
3   3   A03   B03      3      5
4   4   A04   B04      4      7
5   5   A05   A05      5      2

Here's the for-loop that's very slow (with or without the if-clauses activated):

ids<-unique(data$id)
ct<-length(ids)
codes<-matrix(0,ct,11)
colnames(codes)<-c("ID","ICD1","Coder1","ICD2","Coder2","ICD3","Coder3","ICD4","Coder4","ICD5","Coder5")
j<-0
for (i in 1:ct){
  kkk <- ids[i] 
  rpt<-data[data$id==kkk,]
  j<-max(j,nrow(rpt))
  codes[i,1]<-kkk
  codes[i,2]<-rpt$ICDCode[1]
  codes[i,3]<-rpt$T_Physician_ID[1]
  #if (nrow(rpt)>=2){
   codes[i,4]<-rpt$ICDCode[2]
   codes[i,5]<-rpt$T_Physician_ID[2] 
    #if (nrow(rpt)>=3) {
     codes[i,6]<-rpt$ICDCode[3]
     codes[i,7]<-rpt$T_Physician_ID[3]
      #if (nrow(rpt)>=4) {
       codes[i,8]<-rpt$ICDCode[4]
       codes[i,9]<-rpt$T_Physician_ID[4]
          #if (nrow(rpt)>=5) {
           codes[i,10]<-rpt$ICDCode[5]
           codes[i,11]<-rpt$T_Physician_ID[5]
#}}}}
}