R help - Mar 2012 - Noob question - Identity argument within aggregate function?

>aggregate(z, identity, mean)
  1   2   3   4   5 
1.0 3.0 5.0 6.0 7.5 
> aggregate(z, mean)
Error: length(time(x)) == length(by[[1]]) is not TRUE

Can someone help me understand the error above and why "identity" is
necessary to satisfy the error




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Hi,

On Fri, Mar 2, 2012 at 3:51 PM, knavero <knavero at gmail.com>
wrote:
>>aggregate(z, identity, mean)
> ?1 ? 2 ? 3 ? 4 ? 5
> 1.0 3.0 5.0 6.0 7.5
>> aggregate(z, mean)
> Error: length(time(x)) == length(by[[1]]) is not TRUE
>
> Can someone help me understand the error above and why "identity"
is
> necessary to satisfy the error
We can tell you to read ?aggregate and look at the order of the arguments.
We can point out that aggregate(z, mean) is not the same as mean(z), and
wonder what you are trying to accomplish with the former.

We can ask for a reproducible example, and some idea of what you are
trying to do.

Sarah


-- 
Sarah Goslee
http://www.functionaldiversity.org

On Mar 2, 2012, at 3:51 PM, knavero wrote:
>> aggregate(z, identity, mean)
>  1   2   3   4   5
> 1.0 3.0 5.0 6.0 7.5
>> aggregate(z, mean)
> Error: length(time(x)) == length(by[[1]]) is not TRUE
As generally happens when you call a function and fail to provide  
enough arguments to fill up its formals list.
>
> Can someone help me understand the error above and why "identity"
is
> necessary to satisfy the error
Well on my machine it throws an error, probably because you failed to  
provide the requested code to create the objects you were working on.  
Is 'z' so sort of special classed object for which there is an  
aggregate method? Is 'identity' a list as expected by  
aggregate.default or aggregate.data.frame? It would be an unfortunate  
choice of an object name, since there is a function with that nam.

-- 
David Winsemius, MD
West Hartford, CT

z is a zoo object as a result from reading in the following series

z = suppressWarnings(zoo(1:8), c(1, 2, 2, 2, 3, 4, 5, 5))

This is what z is in the aggregate function. So then that brings us to
"aggregate(z, identity, tail, 1)". All I was trying to accomplish was
trying
to reproduce an example shown on the zoo faq. I've read ?aggregate via
terminal and used "/identity" to search through the documentation for
the
specific term "identity". I'm just trying to understand what
identity is
used for because I do not understand the error statement. 



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Sorry, in regards to the previous post where I said aggregate(z, identity,
tail, 1), replace it with aggregate(z, identity, mean)

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