[R] Repeat a loop until...

[Petr PIKAL]

Hi

I may be completely off track without knowing mnormt package but what 
about using while loop for counting rows in "correct" datamat.

#first set your matrix
datamat <- 
rmnorm(n=1500,mean=c(mean(sanad[,1]),mean(sanad[,2]),mean(sanad[,3])),varcov=covmat)

#get rid of out of spec values
datamat <- datamat[(datamat[,2] >5) & (datamat[,2] < 86),] 

# fill further rows
while(nrow(datamat)<1500) {
dat.temp <- rmnorm(n = 1500-nrow(datamat) 
,mean=c(mean(sanad[,1]),mean(sanad[,2]),mean(sanad[,3])),varcov=covmat)
datamat <- rbind(datamat, dat.temp)
}

Regards
Petr



> 
> Dear all,
> 
> I know there have been various questions posted over the years about 
loops
> but I'm afraid that I'm still stuck.  I am using Windows XP and R 2.9.2.
> I am generating some data using the multivariate normal distribution 
> (within the 'mnormt' package). [The numerical values of sanad and covmat 

> are not important.]
> > datamat <- rmnorm(n=1500,mean=c(mean(sanad[,1]),mean(sanad[,2]),mean
> (sanad[,3])),varcov=covmat)
> 
> The middle column of 'datamat' is simulated data for age.  Obviously 
some 
> of the simulated values are not going to be sensible.  Therefore I'd 
like 
> to set up a function that looks at each row of 'datamat' and if the 
value 
> for the middle column is <5 or >86 then the whole row is replaced by 
> another imputed row.  Of course, the problem is that the imputed value 
for
> age may be outside my acceptable range too.
> 
> If there a way to set up a loop such that it keeps checking each row 
until
> the values are within the range?
> 
> So far I have the following but this doesn't repeat the process.
> ctstrunk <- function(data)
>                 {
>                 for(i in 1:nrow(data)){
>                 if(data[i,2]<5)
>                 data[i,]<-rmnorm(n=1,mean=c(mean(sanad[,1]),mean(sanad[,
> 2]),mean(sanad[,3])),varcov=covmat)
>                 if(data[i,2]>86)
>                 data[i,]<-rmnorm(n=1,mean=c(mean(sanad[,1]),mean(sanad[,
> 2]),mean(sanad[,3])),varcov=covmat)
>                 }
>                 return(data)
>                 }
> 
> I thought of perhaps a repeat loop such as the following but this loop 
> never stops...
> ctstrunk <- function(data)
>                 {
>                 repeat{
> for(i in 1:nrow(data)){
>                 if(data[i,2]<5)
>                 data[i,]<-rmnorm(n=1,mean=c(mean(sanad[,1]),mean(sanad[,
> 2]),mean(sanad[,3])),varcov=covmat)
>                 if(data[i,2]>5){break}
>                 }
>                 repeat{
> for(i in 1:nrow(data)){
>                 if(data[i,2]>86)
>                 data[i,]<-rmnorm(n=1,mean=c(mean(sanad[,1]),mean(sanad[,
> 2]),mean(sanad[,3])),varcov=covmat)
>                 if(data[i,2]<86){break}
>                 }
>                 return(data)
>                 }
> 
> I have also tried a while loop but again, the function didn't stop
> ctstrunk <- function(data)
>                 {
>                 for(i in 1:nrow(data)){
>                 while(data[i,2]<5) 
data[i,]<-rmnorm(n=1,mean=c(mean(sanad
> [,1]),mean(sanad[,2]),mean(sanad[,3])),varcov=covmat)
>                 while(data[i,2]>86) 
data[i,]<-rmnorm(n=1,mean=c(mean(sanad
> [,1]),mean(sanad[,2]),mean(sanad[,3])),varcov=covmat)
>                 }
>                 return(data)
>                 }
> 
> Many thanks for any assistance you can offer.
> 
> Kind regards,
> Laura
> 
> Laura Bonnett
> Research Assistant
> Department of Biostatistics
> University of Liverpool
> 
> Telephone: 0151 7944059
> Email: L.J.Bonnett at liv.ac.uk
> 
> 
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> 
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