[R] Odp: How to generate a new column according to some rule?

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 30.03.2009 05:17:35:

> In a data frame I have a column "date" and a column "time",now I want
> to generate a new column which is the mean of the value of time group
> by date. In stata the command is
> 
> egen scalls = mean(time),by(date)
> 
> but I don't know the command in R, can anybody help me?

In R you can use 

?tapply
?by
?aggregate

from base or functions from
?doBy package.

Regards
Petr



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