Hi, people.
I am using R-2.5.0 now, when tried the function aggregate with sum, it
showed an  error as following:
> a <- gl(3,10)
> b <- rnorm(30)
> aggregate(b,list(a),sum)
#  here is the error message,  it complained that an error in FUN(X[[1L]],
missing "INDEX", and no defaults value.

but the tapply function will be okay.
> tapply(b,list(a),sum)
        1         2         3
 2.113349 -5.972195  4.854731

furthermore, when I was using the R-2.5.0 pre-release version before.
it could work well.
> a <- gl(3,10)
> b <- rnorm(30)
> aggregate(b,list(a),sum)      # it works well
  Group.1          x
1       1 -1.0330482
2       2  0.1235796
3       3 -1.0086930
> tapply(b,list(a),sum)            # so does tapply
         1          2          3
-1.0330482  0.1235796 -1.0086930

So, who can tell what should I do to overcome this?
thanks a lot.

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