[R] Exchange NAs for mean

[Chuck Cleland]

On 12/17/2009 9:31 AM, Joel Fürstenberg-Hägg 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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-- 
Chuck Cleland, Ph.D.
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