Thank you all for your help,
This is what I was able to do

aggregate(items,items[2],mean)


Where items has all my data, and items[2] has my group id number.
Here are my 2 questions

1) items[1] has a unquie number in it, how do I tell mean to take the mean
of items[3] not items[1]
2) Is there an easy way to add a count of items[1] for each items[2].  In
other words, when it aggregates, I want to know how many items are in each
group.


Thanks,
Lotta

On Fri, Aug 1, 2008 at 2:47 PM, Jorge Ivan Velez
<jorgeivanvelez@gmail.com>wrote:

>
> Dear Lotta,
>
> Try
>
> my.df <- data.frame(a <- c(1,6,10,11,3,5,10), group <- c(5,5,5,5,9,9,9))
> tapply(my.df$a,my.df$group,median)
> 5 9
> 8 5
>
> See ?tapply and/or ?aggregate for more information.
>
> HTH,
>
> Jorge
>
>
>
>
>  On Fri, Aug 1, 2008 at 1:30 PM, Lotta R <lottajane@gmail.com> wrote:
>
>>  Hi all,
>>
>> I have data that looks like
>>
>> number|grouping
>>
>>
>> I would like to preform stats for each grouping
>>
>> so
>>
>> 1|5
>> 6|5
>> 10|5
>> 11|5
>> 3|9
>> 5|9
>> 10|9
>>
>> Say I would like to take the median for above, I should be returned 2
>> lines,
>> one for group #5 and one for group #9
>>
>> Does this make sense?
>>
>> I am sorry for the basic question, can someone give me the name of a good
>> book as well?
>>
>> Thanks,
>> Lotta
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>

	[[alternative HTML version deleted]]

