Turn NULL objects into usable objects in a dataframe

Question

I am going through a model selection exercise where I am running a model that loops the number of parameters to add to the model. Some parameters in the model are returned as NULL meaning the model did not converge and there was some sort of problem. Obviously this is an issue. However my problem is that the NULL values wreak havoc with creating a readable dataframe. Without a dataframe that captures where the NULL values are it is difficult to troubleshoot the problem. So a long preamble to ask how do I make a returned NULL object an NA or a character NULL such that the dataframe can still be created. Here is an example:

R = 10
m = 5
lik = NULL


data.frame(R=R,
           m=m, 
           lik=lik)

This return this error:

Error in data.frame(R = R, m = m, lik = lik) : arguments imply differing number of rows: 1, 0

I have tried using as.numeric(lik) or as.character(lik) but neither of those have produced the desired effect.

Any ideas how to deal with this?

How if is.null() along with some sort of an ifelse based assignment of NA? — Gopala
– Gopala, Commented Apr 13, 2016 at 17:52

Lars Arne Jordanger · Accepted Answer · 2016-04-13 17:53:00Z

3

You can try:

R = 10
m = 5
lik = NULL


data.frame(R=R,
           m=m, 
           lik= if (is.null(lik)) {
               "NULL"
           } else
               lik
           )

answered Apr 13, 2016 at 17:53

Lars Arne Jordanger

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