extracting data from a weird looking object in R script - r

Question

In my R script...
I have an object myObject which is something that looks like this:
> myObject
m convInfo data call dataClasses control
FALSE FALSE FALSE FALSE FALSE FALSE
It is what is returned from an is.na(obj) where obj is an nls fit.
I'm trying to test if that first item is FALSE rather than TRUE. How can I extract that out? I tried myObject$m but that didn't work.

Answer 1

You have a named (logical) vector.
> v <- 1:5
> names(v) <- LETTERS[1:5]
> is.na(v)
A B C D E
FALSE FALSE FALSE FALSE FALSE
> myObj <- .Last.value
You address it like any other atomic vector:
> myObj[1]
A
FALSE
> myObj[1] == FALSE
A
TRUE

Answer 2

The object returned by nls() is a list. The behaviour of is.na() on a list is somewhat peculiar in the sense of what is an is not NA. From ?is.na:
Value:
The default method for ‘is.na’ applied to an atomic vector returns
a logical vector of the same length as its argument ‘x’,
containing ‘TRUE’ for those elements marked ‘NA’ or, for numeric
or complex vectors, ‘NaN’ (!) and ‘FALSE’ otherwise. ‘dim’,
‘dimnames’ and ‘names’ attributes are preserved.
The default method also works for lists and pairlists: the result
for an element is false unless that element is a length-one atomic
vector and the single element of that vector is regarded as ‘NA’
or ‘NaN’.
So t is a logical vector with the TRUE & FALSE values in your t determined as per the quoted text above. Therefore all of
t[1]
t["m"]
head(t, 1)
extract the first element of t. If you want to test for FALSE then I might try:
!isTRUE(t[1])
E.g.
> set.seed(1)
> logi <- sample(c(TRUE,FALSE), 5, replace = TRUE)
> logi
[1] TRUE TRUE FALSE FALSE TRUE
> !isTRUE(logi[1])
[1] FALSE
The reason the $ version won't work is that $ is documented to apply only to non-atomic vectors. logi (or your t) is an atomic vector, in that it contains elements of the same type.
> is.atomic(logi)
[1] TRUE
> names(logi) <- letters[1:5]
> logi$a
Error in logi$a : $ operator is invalid for atomic vectors
> logi["a"]
a
TRUE