[R] Question on summing rows within nested variable

[jim holtman]

If you want zero if only one variable:

> DF2
  sid pid slope
1 1.1 1.1     2
2 1.1 4.1     3
3 1.1 5.1     2
4 2.1 5.1     3
5 3.2 1.2     2
6 3.2 1.7     3
> tapply(DF2$slope, DF2$sid, function(x) if(length(x) == 1) 0 else mean(x))
     1.1      2.1      3.2
2.333333 0.000000 2.500000
>


On Fri, Mar 13, 2009 at 6:43 PM, Vedula, Satyanarayana
<svedula at jhsph.edu> wrote:
> Hi,
>
> I was hoping someone could help figure out how to write code for R to do the below.
>
> I have data that looks like below. Variables, sid and pid are strings, slope is numeric. I need R to get me the mean of slopes for all pid's nested within each sid if there are more than one pid's nested within sid.
>
> If there is only pid for a sid, like for 2.1 below, I want R to write a 0.
>
> In the data below, I want to get the mean of slopes for pid (1.1; 4.1; and 5.1) because they are nested within sid 1.1 and so on.
>
> Thanks in advance for any suggestions.
> Swaroop
>
> sid        pid        slope
> 1.1        1.1        2
> 1.1        4.1        3
> 1.1        5.1        2
> 2.1        5.1        3
> 3.2        1.2        2
> 3.2        1.7        3
>
>
>
>
>        [[alternative HTML version deleted]]
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?