[R] More flexible aggregate / eval

[David Winsemius]

On Apr 30, 2011, at 7:06 AM, Patrick Hausmann wrote:

> Dear list,
>
> I would like to do some calculation using different grouping  
> variables. My 'df' looks like this:
>
> # Some data
> set.seed(345)
> id <- seq(200,400, by=10)
> ids <- sample(substr(id,1,1))
> group1 <- rep(1:3, each=7)
> group2 <- rep(1:2, c(10,11))
> group3 <- rep(1:4, c(5,5,5,6))
> df <- data.frame(id, ids, group1, group2, group3)
> df <- rbind(df, df, df)
> df$time <- seq(2009, 2011, each=3)
> df$x1 <- sample(0:100, 63)
> df$x2 <- sample(44:234, 63)
>
> head(df)
>
> ## For group1
> d1 <- aggregate(cbind(x1, x2) ~
>                      group1 + ids + time, data = df, sum)
>
> d1$l_pct <- with(d1, ave(x1, list(group1, time),
>                 FUN = function(x) round(prop.table(x) * 100, 1) ) )
>
> op1 <- xtabs(l_pct ~ group1 + ids + time, data = d1)
> ftable(op1, row.vars=c(1,3))
>
> ## For group2
> d2 <- aggregate(cbind(x1, x2) ~
>                      group2 + ids + time, data = df, sum)
>
> d2$l_pct <- with(d2, ave(x1, list(group2, time),
>                 FUN = function(x) round(prop.table(x) * 100, 1) ) )
>
> op2 <- xtabs(l_pct ~ group2 + ids + time, data = d2)
> ftable(op2, row.vars=c(1,3))
>
> ## and for group3...
> ## To have a more flexible solution I wrote this function:
>
> myfun <- function(xdf, xvar) {
>
> fo1 <- "cbind(x1, x2) ~ "
> fo2 <- paste(fo1, xvar, "+ ids + time", sep="")
> formular <- as.formula(fo2)
>
> d2 <- do.call(aggregate, list(formular, data = xdf, FUN = sum))
>
> d2$l_pct <- with(d2, ave(x1, list(eval(as.name(xvar)), time),
>                  FUN = function(x) round(prop.table(x) * 100, 1) ) )
> op2 <- xtabs(l_pct ~ eval(as.name(xvar)) + ids + time, data = d2)
> fop2 <- ftable(op2, row.vars=c(1,3))
> out <- list(d2, fop2)
> return(out)
>
> }
>
> ( out_gr1 <- myfun(df, "group1") )
> ( out_gr2 <- myfun(df, "group2") )
> ( out_gr3 <- myfun(df, "group3") )
>
> This seems to work ok, but I am not really familiar with  
> 'as.formula', 'eval' and 'as.name'. So I would like to know, if my  
> solution is ok or if there are maybe better ways to solve this task.

The do.call to aggregate looks unnecessarily complex and could be  
changed to:

d2 <- aggregate(formular, data = xdf, FUN = sum)


-- 
David Winsemius, MD
West Hartford, CT