R help - Dec 2009 - Exchange NAs for mean

Hi all,

 

I'm have a matrix (X) with observations as rows and parameters as columns.
I'm trying to exchange all missing values in a column by the column mean
using the code below, but so far, nothing happens with the NAs... Can anyone see
where the problem is?

 

N<-nrow(X) # Calculate number of rows = 108
p<-ncol(X) # Calculate number of columns = 88
   

# Replace by columnwise mean
for (i in colnames(X)) # Do for all columns in the matrix
{ 
   for (j in rownames(X)) # Go through all rows
   {
      if(is.na(X[j,i])) # Search for missing value in the given position
      {
         X[j,i]=mean(X[1:p, i]) # Change missing value to the mean of the column
      }
   }
} 

 

All the best,

 

Joel

 


 
 		 	   		  
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2009/12/17 Joel F?rstenberg-H?gg <joel_furstenberg_hagg at
hotmail.com>:
>
> Hi all,
>
>
>
> I'm have a matrix (X) with observations as rows and parameters as
columns. I'm trying to exchange all missing values in a column by the column
mean using the code below, but so far, nothing happens with the NAs... Can
anyone see where the problem is?
>
>
>
> N<-nrow(X) # Calculate number of rows = 108
> p<-ncol(X) # Calculate number of columns = 88
>
>
> # Replace by columnwise mean
> for (i in colnames(X)) # Do for all columns in the matrix
> {
> ? for (j in rownames(X)) # Go through all rows
> ? {
> ? ? ?if(is.na(X[j,i])) # Search for missing value in the given position
> ? ? ?{
> ? ? ? ? X[j,i]=mean(X[1:p, i]) # Change missing value to the mean of the
column
> ? ? ?}
> ? }
> }
>

 mean(anything with an NA in it) == NA. You want mean(X[1:p,i],na.rm=TRUE)

 > mean(c(1,2,3,NA,4))
 [1] NA
 > mean(c(1,2,3,NA,4),na.rm=TRUE)
 [1] 2.5

I'll leave it to someone else to show you how to speed this code up by
removing the loops...

Barry

On 12/17/2009 9:31 AM, Joel F?rstenberg-H?gg wrote:
> Hi all,
> 
>  
> 
> I'm have a matrix (X) with observations as rows and parameters as
columns. I'm trying to exchange all missing values in a column by the column
mean using the code below, but so far, nothing happens with the NAs... Can
anyone see where the problem is?
> 
>  
> 
> N<-nrow(X) # Calculate number of rows = 108
> p<-ncol(X) # Calculate number of columns = 88
>    
> 
> # Replace by columnwise mean
> for (i in colnames(X)) # Do for all columns in the matrix
> { 
>    for (j in rownames(X)) # Go through all rows
>    {
>       if(is.na(X[j,i])) # Search for missing value in the given position
>       {
>          X[j,i]=mean(X[1:p, i]) # Change missing value to the mean of the
column
>       }
>    }
> } 
> mymat <- matrix(runif(50), ncol=5)
> mymat[c(3,4,9),c(1,2,5)] <- NA
> mymat
            [,1]       [,2]       [,3]       [,4]      [,5]
 [1,] 0.05863667 0.23545794 0.25549983 0.96275422 0.1015316
 [2,] 0.66107818 0.15846239 0.05112992 0.09081990 0.6097318
 [3,]         NA         NA 0.86474629 0.73186676        NA
 [4,]         NA         NA 0.26226776 0.31987242        NA
 [5,] 0.78472732 0.09072242 0.24557669 0.57100857 0.1568413
 [6,] 0.42431343 0.37551338 0.86085073 0.62782597 0.5090823
 [7,] 0.44609972 0.90125504 0.52285650 0.41298482 0.3192929
 [8,] 0.27676684 0.17200162 0.70648140 0.86983249 0.2035595
 [9,]         NA         NA 0.34956846 0.07070571        NA
[10,] 0.01482263 0.20074897 0.41553916 0.82367719 0.9674044
> apply(mymat, 2, function(x){x <- replace(x, is.na(x), mean(x,
na.rm=TRUE))})
            [,1]       [,2]       [,3]       [,4]      [,5]
 [1,] 0.05863667 0.23545794 0.25549983 0.96275422 0.1015316
 [2,] 0.66107818 0.15846239 0.05112992 0.09081990 0.6097318
 [3,] 0.38092069 0.30488025 0.86474629 0.73186676 0.4096348
 [4,] 0.38092069 0.30488025 0.26226776 0.31987242 0.4096348
 [5,] 0.78472732 0.09072242 0.24557669 0.57100857 0.1568413
 [6,] 0.42431343 0.37551338 0.86085073 0.62782597 0.5090823
 [7,] 0.44609972 0.90125504 0.52285650 0.41298482 0.3192929
 [8,] 0.27676684 0.17200162 0.70648140 0.86983249 0.2035595
 [9,] 0.38092069 0.30488025 0.34956846 0.07070571 0.4096348
[10,] 0.01482263 0.20074897 0.41553916 0.82367719 0.9674044
> All the best,
> 
>  
> 
> Joel
> 
>  
> 
> 
>  
>  		 	   		  
> _________________________________________________________________
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