[R] SAPPLY function XXXX

[Erik Iverson]

Dan,


> I am attempting to write a function to count the number of non-missing
> values of each column in a data frame using the sapply function. I have the
> following code which is receiving the error message below.
> 
> 
>> n.valid<-sapply(data1,sum(!is.na))
> Error in !is.na : invalid argument type

That's the FUN argument to sapply, which expects a function.  is.na is 
indeed a function, but !is.na is not a function:

 > !is.na
Error in !is.na : invalid argument type

You need to write your own function to do what you want. Luckily this is 
easy. Let's write one to count the number of missing values in a vector.

countNAs <- function(x) {
    sum(!is.na(x))
}

Now you have a function that does what you want, so you can use sapply 
with it.

sapply(data1, countNAs)

You could also do an anonymous (unnamed) function within sapply to the 
same effect.

sapply(data1, function(x) sum(!is.na(x)))

NB: none of this is tested!

--Erik


> 
> Ultimately, I would like for this to be 1 conponent in a larger function
> that will produce PROC CONTENTS style output. Something like...
> 
> data1.contents<-data.frame(Variable=names(data1),
>  Class=sapply(data1,class),
>  n.valid=sapply(data1,sum(!is.na)),
>  n.miss=sapply(data1,sum(is.na)))
> data1.contents
> 
> Any suggestions/assistance are appreciated.
> 
> Thank you,
> 
> Daniel
> 
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> 
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