Help rewriting looping structure?

Hey Folks,

Could somebody help me rewrite the following code?

I am looping through all records across 5 fields to calculate the
cumulative
percentage of each record (relative to each individual field).

Is there a way to rewrite it so I don't have to loop through each
individual
record?

##### tdat is my data frame
##### j is my field index
##### k is my record index
##### tsum is the sum of all values in field j
##### tmp is a vector containing the values in field j
##### tdat[k,paste("cpct,j,sep="")] creates new fields "cpct1",...,"cpct5" 


for(j in 1:5) {
  tsum<- sum(tdat[,j]);
  for(k in 1:nrow(tdat)) {
    td<- tdat[k,j];
    tmp<-tdat[,j];
##### sum values <= to current value and divide by the total sum
    tdat[k,paste("cpct,j,sep="")]<- sum(tmp[tmp <= td]) / tsum;
  }
}


Thanks,
TLowe