# Finding the sum of repeated continuous variables for each subject

Suppose you have a data set with repeated measures --- i.e., you have multiple values of a continuous variable (e.g., `var1` and `var2` below) for each subject in your data set (each subject could have a different number of records).

```d = data.frame(d=c(1,1,1,2,2,4,4,4), var1 = round(rnorm(8),1 ),
var2 = c(round(rnorm(8),1)))
d
```

You would like to find the sum of the repeated `var1` and `var2` values for each subject and you would like to keep these results in your original repeated measures data frame.

Here's the 'solution:'

```varList = c("var1", "var2")
for (n in varList){
t = tapply(d[[n]], d\$id, sum, na.rm=TRUE)
d[[paste("sum",n,sep="")]] = t[as.character(d\$id)]
}
d
```

This problem and solution were posted by Svetlana Eden.
Topic revision: r2 - 21 Nov 2006, TheresaScott

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