[R] storing element number of a list in a column data frame

[Bert Gunter]

Have you read An Introduction to R (ships with R) or another of the
many excellent R tutorials on the web? I ask, because you do not
appear to be using a sensible data structure. As your list appears to
be of a single type (probably numeric, maybe integer), it would be
preferable to use a vector, like this:

y <- c(45, NA, 18, NA, 99)

(The NULLS must be converted to NA's to "hold" their places).

There would then seem to be little need for the data frame structure,
as it tends to slow things down in R. But if you insist,

which(is.na(y))

will give you the indices of the NA's.

See also: ?is.na  ?is.null.


Cheers,
Bert



On Thu, Oct 3, 2013 at 7:41 AM, Massimo Bressan <mbressan at arpa.veneto.it> wrote:
> #let's suppose I have a list like this
>
> mytest<-list(45, NULL, 18, NULL, 99)
>
> #to note that this is just an amended example because in fact
>
> #I'm dealing with a long list (more than 400 elements)
>
> #with no evident pattern of the NULL values
>
> #I want to end up with a data frame like the following
>
> data.frame(i=c(1,3,5), n=c(45,18,99))
>
> #i.e. a data frame storing in
>
> #column i the number of corresponding element list
>
> #column n the unique component of that element
>
> #I've been trying with
>
> do.call(rbind, mytest)
>
> #or
>
> do.call(rbind.data.frame, mytest)
>
> #but this approach is not properly achieving the desired result
>
> #now I'm in trouble on how to store each element number of the list in
> the first column data frame
>
> #any help for this?
>
> #thanks
>
>
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>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

(650) 467-7374