This is a very commonly used paradigm in R and there are many
different answers, one would be tapply(). You could also look at the
plyr package.
Michael
On Sat, Mar 24, 2012 at 11:32 AM, reeyarn <reey...@gmail.com> wrote:
> Hi, I want to run something like
> SELECT firm_id, count(*), mean(value), sd(value)
> FROM table
> GROUP BY firm_id;
>
> But I have to write a for loop like
> for ( id in unique(table$firm_id ) {
> print(paste( id, mean(table[firm_id == id, "value"]) ))
> }
>
> Is there any way to do it easier? Thanks :)
>
>
> Best,
> Reeyarn Lee
>
> [[alternative HTML version deleted]]
>
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