[R] how to ignore NA with "NA" or "NULL"

[jeff6868]

Hello dear R-users,

I have a problem in my code about ignoring NA values without removing them.
I'm working on a list of files. The aim is to fill one file from another
according to the highest correlation (correlation coeff between all my
files, so the file which looks like the most to the one I want to fill).
When I have just small gaps of NA, my function works well.
The problem is when I have only NAs in some files. As a consequence, it
cannot calculate any correlation coefficients (my previous function in the
case of only NAs in the file returns "NA" for the correlation coefficient),
and so it cannot fill it or make any calculation with it.

Nevertheless in my work I need to keep these NA files in my list (and so to
keep their dimensions). Otherwise it creates some dimensions problems, and
my function needs to me automatic for every files.

So my question in this post is: how to ignore (or do nothing with them if
you prefer) NA files with NA correlation coefficients?
The function for filling files (where there's the problem) is:

na.fill <- function(x, y){        
        i <- is.na(x[1:8700,1])
        xx <- y[1:8700,1]             
        new <- data.frame(xx=xx)       
        x[1:8700,1][i] <- predict(lm(x[1:8700,1]~xx, na.action=na.exclude),
new)[i]
        x        
    }

My error message is: Error in model.frame.default(formula = x[1:8700, 1] ~
xx, na.action = na.exclude,  :  : invalid type (NULL) for variable 'xx'

I tried to add in the function:  
ifelse( all(is.null(xx))==TRUE,return(NA),xx)  or
ifelse( all(is.null(xx))==TRUE,return(NULL),xx)

but it still doesn't work.
How can I write that in my function? With NA, NULL or in another way?
Thank you very much for your answers


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