[R] how to assign a group mean to individual cases?

[Emmanuel Charpentier]

Answering to myself...
Emmanuel Charpentier a écrit :
> Casey Klofstad a écrit :
>> I need advice on how to create a variable that is the group mean of
>> another variable.
>>
>> For example, I have a variable called x for which each row in the data
>> set has a value. I also have a nominal variable called g that
>> indicates which of 100 different groups each row belongs to.
>>
>> So, I want to create a new variable called w, which is the group mean
>> of x for which ever group the row belongs to (as indicated by variable
>> g). Ideally, I'd also like to take out each row's value of x before
>> calculating the group mean assigned to that row.
>>
>> I've already tried the aggregate command. That gives me the group
>> means, but does not allow me to assign them to each row in the data
>> set.
> 
> The first one is easy : you just have to choose which siege cannon you
> need to shoot your fly. What about :
> 
> your.dataset$w<-(aov(x~g,data=your.dataset))$fitted.values
> 
> No a priori idea about the second one, but it has a strong flavor of
> jackknife ; I'd have a look in this direction...

A bit of seaching my aging memory led me to

?lm.influence

whose "coefficients" component might be exploited to get what you mean.

But maybe you are trying to reinvent lm.influence ?

					Emmanuel Charpentier