[R] Managing a list with a list

[abunn@mymail.msu.montana.edu]

OK. Another amateur question.

I have a list with attributes on pine trees, like the stem's location, a logical value set to T if it's alive, some parameters for growth, diameter, etc. The tree list has another list in it which is a new data type for me. 

I want to make a new list that retains all the live trees. 
That is where Living == T.

Here's the summary of the list:

> summary(tf)
       Length Class  Mode   
id     10     -none- numeric
x      10     -none- numeric
y      10     -none- numeric
A      10     -none- numeric
NegB   10     -none- numeric
K      10     -none- numeric
Age    10     -none- numeric
DBH    10     -none- numeric
Living 10     -none- logical
pSeed  10     -none- list   
TCI    10     -none- numeric
STA    10     -none- numeric

Here are the living trees.

> tf$Living
 [1] FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE

So, here are the ids of the trees I want to retain.

> tf$id[tf$Living == T]
[1]  2  3  4  5  6  7  9 10

Same with the easting coordinates.

> tf$x[tf$Living == T] #tf[[2]][tf$Living == T]
[1] 28 35 18 34 36 92  3 47
> 

But when I try to keep the whole list minus the dead trees it returns a list with all the trees living and dead (as I'm sure it is supposed to):

tf[tf$Living == T]

What am I doing wrong? I'm happy to RTFM, but if the manual in question is section 3.4 of R-lang then I'm still going to need help. I can break it all apart and then concatonate a new list but that seems heavy handed.

Thanks, Andy