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[Bioc-devel] Problem with subset("AnnDbBimap", ...) ?

6 messages · Hervé Pagès, Laurent Gautier

#
Dear list,

The function subset("AnnDbBimap", ...) is returning an error whenever 
the resulting subset should be the empty set.

Example:

library(mouse4302.db)
subset(mouse4302SYMBOL,
        Rkeys="foo")


returns:
Error in .checkKeys(value, Rkeys(x), x at ifnotfound) :
   value for "foo" not found

This is true for either Lkeys or Rkeys.


The man page does say "
Lkeys
The new Lkeys (must be a subset of the current Lkeys).

Rkeys
The new Rkeys (must be a subset of the current Rkeys).
"

but this is limiting the use for the function and encourages the use of 
the environment-like API, although marked as provided "for backward 
compatibility".

Wouldn't it be good to either have:

- have subset return without an error

- have at least functions such as hasLkey and hasRkey ?



L.
#
Hi Laurent,

All this is consistent. One important part of the contract for
subset(), Lkeys<-, Rkeys<-, [ is that they behave like endomorphisms
i.e. they return an instance of the same class as the original
object.
mouse4302SYMBOL is an AnnDbBimap object so any of the functions above
must return a (valid) AnnDbBimap object.
The keys of a valid AnnDbBimap object cannot be anything. For example
if 'x' is a mapping from probeset ids to entrez ids, the left keys
must be valid probeset ids (for this chip) and the right keys must be
valid entrez ids.
What kind of AnnDbBimap object would be returned by
subset(mouse4302SYMBOL, Rkeys="foo") ? Or equivalently, what
kind of AnnDbBimap object would become 'x' after
   x <- mouse4302SYMBOL; Rkeys(x) <- "foo".
It would be an AnnDbBimap object with junk keys but valid
AnnDbBimap objects don't support this.

I added these functions when I worked on faking the environment
interface for SQLite-based annotations. Note that they are not
part of the environment-like API. They are low-level
functions that I first wrote and used internally so it would
be easier for me to build the environment-like API (mget, get,
ls, etc...). My first intention was not to export them but then
I realized they had their own added-value so I exported and
documented them. Since they are not part of the environment-like
API, I had no constraint of backward compatibility which was nice
because then I could decide to make them do what I considered the
right thing. OTOH I had to make the environment-like API ackward
compatible and that's why you can use junk keys in mget (granted
that you specify ifnotfound=NA):

   > mget("foo", mouse4302SYMBOL, ifnotfound=NA)
   $foo
   [1] NA

mget() returns a list, not an AnnDbBimap instance (it's not an
endomorphism) so it can return a list with anything in it without
breaking any rule.

We could add the hasLkey() and hasRkey() but since this would be
equivalent to "foo" %in% Rkeys(x), I'm not sure they would have
a lot of added value though. The performance of "foo" %in% Rkeys(x)
should be good enough, especially the 2nd time you do this on 'x'
because Rkeys() (like Lkeys() and other low-level functions in
AnnotationDbi) cache their result (in a hidden environment).

H.
Laurent Gautier wrote:

  
    
#
Hi Herv?,

Thanks for for detailled answer.

I understand that the choice was made to forbid the addition of 
[L|R]keys to a Bimap (which you call "junk keys"). I suspect that
implementation concerns weighted in the decision, but that's for a
separate thread.

Unless the message is that the environment-like API is not around only 
for back-compatibility reasons, the main (consistency) problem I am 
having with subset("AnnDbBimap", ...) is  still present after reading 
your explanations, although it might be coming from the use of the 
function subset in R's base working on data.frame.

I'll illustrate it with an example:
[1] Plant     Type      Treatment conc      uptake
<0 rows> (or 0-length row.names)

The function subset("data.frame", ...) is then no less endomorphic than
subset("AnnDbBimap", ...), yet it returns an empty data.frame rather 
than raise an error such as 'no "unfair" Treatment'.

In its current instance, the function subset("AnnDbBimap", ...) might be 
pushing complexity toward the user for use-cases such as:
"I have a list of arbitrary gene symbols, and I'd like to get the
probes/probesets associated with those".

The current (as of today) implementation for subset("Bimap", ...) is:

setMethod("subset", "Bimap",
     function(x, Lkeys=NULL, Rkeys=NULL)
     {
         Lkeys(x) <- Lkeys
         Rkeys(x) <- Rkeys
         x
     }
)

while it could be like:

setMethod("subset", "Bimap",
     function(x, Lkeys=NULL, Rkeys=NULL, quiet=FALSE)
     {
         if (quiet) {
             Lkeys(x) <- Lkeys[Lkeys %in% Lkeys(x)]
             Rkeys(x) <- Rkeys[Rkeys %in% Rkeys(x)]
         } else {
             Lkeys(x) <- Lkeys
             Rkeys(x) <- Rkeys
         }
         x
     }
)


Just a thought,



L.
Herv? Pag?s wrote:
2 days later
#
Hi Laurent,

OK I have to admit that I added "subset" as a convenient way
of reducing the sets of Lkeys and Rkeys in a single call.
But I didn't really take the time to check what "subset" is
doing exactly on data frames and I agree that it should
behave as consistently as possible across data structures.

I'll add the 'quiet' argument to subset("AnnDbBimap", ...).
You suggest to use 'quiet=FALSE' as default so by default
it won't behave like for data frames but I guess at this point
we don't want to make a change that could potentially turn into
less safe code written by people who expect "subset" to check
the validity of their keys.

I'll let you know when the change is ready.

Thanks for the feedback!

H.
Laurent Gautier wrote:

  
    
#
Hi all,

I added the 'drop.invalid.keys' arg to the "subset" methods for Bimap
and AnnDbBimap objects in AnnotationDbi (devel and release):

   > library(hgu95av2.db)
   > subset(hgu95av2SYMBOL, Rkeys="foo")
   Error in .checkKeys(value, Rkeys(x), x at ifnotfound) :
     value for "foo" not found
   > mymap <- subset(hgu95av2SYMBOL, Rkeys="foo", drop.invalid.keys=TRUE)
   > mymap
   SYMBOL submap for chip hgu95av2 (object of class "AnnDbBimap")
   > summary(mymap)
   SYMBOL submap for chip hgu95av2 (object of class "AnnDbBimap")
   |
   | Lkeyname: probe_id (Ltablename: probes)
   |    Lkeys: "1000_at", "1001_at", ... (total=12625/mapped=0)
   |
   | Rkeyname: symbol (Rtablename: gene_info)
   |    Rkeys:
   |
   | direction: L --> R

(Note that an argument named 'quiet' is generally not expected to
modify what a function is doing, only what the function is reporting,
hence the choice of 'drop.invalid.keys' for this arg.)

The new version of AnnotationDbi will propagate to the public repos
in about 24 hours.

Cheers,
H.


Quoting Herv? Pag?s <hpages at fhcrc.org>:
#
hpages at fhcrc.org wrote:
Indeed. The name for the parameter was not very well chosen... not 
chosen at all for the long term in fact, just to illustrate with an 
example what subset() could do.
Thanks for the quick response,


L.