R help - Mar 2009 - Mean-replacing NAs in a 3d array

Hi all

I have a 3d array containing missing values.
> Xa
, , 1

     [,1] [,2]
[1,]    1    3
[2,]   NA    4

, , 2

     [,1] [,2]
[1,]    5    7
[2,]   NA   NA

, , 3

     [,1] [,2]
[1,]    9   11
[2,]   10   12

I want to replace the missing values with the mean, but the mean of each
'page' in the array (wrong terminology I'm sure). So - for the array
above - [2,1,2] and [2,2,2] should both read '6', and [2,1,1] should be
'2.66667'.

I can obtain a vector of those means by:
> colMeans(Xa,na.rm=TRUE,dims=2)
[1]  2.666667  6.000000 10.500000

But what to do next?

Help would be appreciated. Also I'm a noob to this mailing list so
apologies if I've not given enough detail or failed to find the answer
somewhere obvious.

Best
Tom Marshall, Universiteit van Amsterdam

Hi Tom,
it would have been nice (and it is in fact requested by the posting 
guide) to give a running example instead of letting us construct your data.
Anyway, it wasn't too hard with
 Xa<-array(1:12,dim=c(2,2,3))
 Xa[c(2,6,8)]<-NA

#so next, create a vector for the colMeans with length 2*2*3, repeating 
each mean 4 times
cM<-rep(colMeans(Xa,na.rm=TRUE,dims=2),each=dim(Xa)[1]*dim(Xa)[2])

#... and use the fact, that most r-objects have also an one-dimensional 
index (which was used in the construction above as well)
Xa[is.na(Xa)]<-cM[is.na(Xa)]

hth.

T.R. Marshall schrieb:
> Hi all
>
> I have a 3d array containing missing values.
>
>   
>> Xa
>>     
> , , 1
>
>      [,1] [,2]
> [1,]    1    3
> [2,]   NA    4
>
> , , 2
>
>      [,1] [,2]
> [1,]    5    7
> [2,]   NA   NA
>
> , , 3
>
>      [,1] [,2]
> [1,]    9   11
> [2,]   10   12
>
> I want to replace the missing values with the mean, but the mean of each
> 'page' in the array (wrong terminology I'm sure). So - for the
array
> above - [2,1,2] and [2,2,2] should both read '6', and [2,1,1]
should be
> '2.66667'.
>
> I can obtain a vector of those means by:
>   
>> colMeans(Xa,na.rm=TRUE,dims=2)
>>     
> [1]  2.666667  6.000000 10.500000
>
> But what to do next?
>
> Help would be appreciated. Also I'm a noob to this mailing list so
> apologies if I've not given enough detail or failed to find the answer
> somewhere obvious.
>
> Best
> Tom Marshall, Universiteit van Amsterdam
>
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