R help - Oct 2011 - using mean substitution

Hi, all,

I'm running a monte carlo simulation with missing data. The data are
arranged such that there are k columns and n rows over a set number of
simulations (set to 10 right now so it runs fast while I set everything up). The
data are integers, numbers 1-7 only (normal distribution). The simulations are
set up and run without a hitch, including imposing NA missing values at a
specified prevalence semi-randomly (there are not allowed to be any completely
empty rows).

I'd like to replace the missing values ("NA") with the mean for
the non-missing items items *on that row*.  I want to go through all the monte
carlo simulation runs that I already did (so that I'm using the same data)
and replace NA with the mean (e.g., if k=5 and a row has values of 3 3 NA 5 5, I
want to put a 4 in for NA). I also want the imputed mean values to be rounded to
the nearest integer.

Does anyone have an idea for how I'd set that up? I feel like there's a
fairly easy way to set up searching out those NAs and replacing the the row mean
that is not coming to me.

Thanks,
Mike

On 18/10/11 10:35, Michael Parent wrote:
> Hi, all,
>
> I'm running a monte carlo simulation with missing data. The data are
arranged such that there are k columns and n rows over a set number of
simulations (set to 10 right now so it runs fast while I set everything up). The
data are integers, numbers 1-7 only (normal distribution).
     For CRYING OUT LOUD.  This sort of blithering nonsense makes me
     want to SCREAM!!!  The normal distribution is a continuous 
distribution.
     It does not take on (exclusively) integer values.
> The simulations are set up and run without a hitch, including imposing NA
missing values at a specified prevalence semi-randomly (there are not allowed to
be any completely empty rows).
>
> I'd like to replace the missing values ("NA") with the mean
for the non-missing items items *on that row*.  I want to go through all the
monte carlo simulation runs that I already did (so that I'm using the same
data) and replace NA with the mean (e.g., if k=5 and a row has values of 3 3 NA
5 5, I want to put a 4 in for NA). I also want the imputed mean values to be
rounded to the nearest integer.
>
> Does anyone have an idea for how I'd set that up? I feel like
there's a fairly easy way to set up searching out those NAs and replacing
the the row mean that is not coming to me.
Let your matrix of values be "m".

rv <- round(apply(m,1,mean,na.rm=TRUE))
ij <- which(is.na(m),arr.ind=TRUE)
m[ij] <- rv[ij[,1]]

     cheers,

         Rolf Turner