Aggregate NAs in R -

i'm having trouble handling nas while calculating aggregated means. please see following code:

tab=data.frame(a=c(1:3,1:3), b=c(1,2,na,3,na,na)) tab    b 1 1  1 2 2  2 3 3 na 4 1  3 5 2 na 6 3 na  attach(tab) aggregate(b, by=list(a), data=tab, fun=mean, na.rm=true)   group.1   x 1       1   2 2       2   2 3       3 nan 

i want na instead of nan if vector has nas i.e. want output

  group.1   x 1       1   2 2       2   2 3       3  na 

i tried using custom function:

adjmean=function(x) {if(all(is.na(x))) na else mean(x,na.rm=true)} 

however, following error:

aggregate(b, by=list(a), data=tab, fun=adjmean)  error in fun(x[[1l]], ...) :    unused argument (data = list(a = c(1, 2, 3, 1, 2, 3), b = c(1, 2, na, 3, na, na))) 

in short, if column has nas want na output instead of nan. if has few nas, should compute mean ignoring nas.

any appreciated.

thanks

this close had, replaces mean(x, na.rm=true) custom function either computes mean of non-na values, or supplies na itself:

r> with(tab,          aggregate(b, by=list(a), fun=function(x)               if (any(is.finite(z<-na.omit(x)))) mean(z) else na))   group.1  x 1       1  2 2       2  2 3       3 na r>  

that 1 line, broke make fit display.

and had similar idea, altered function bit more return suitable values in cases.