R devel - Aug 2007 - Consistency of serialize(): please enlighten me

Hi,

I am puzzled with serialize().  It comes down generating identical
hash codes for (apparently) identical objects using digest::digest(),
which in turn relies on serialize().  Here is an example illustration
the issue:

ser <- function(object, ...) {
  list(
    names = names(object),
    namesRaw = charToRaw(names(object)),
    ser = serialize(names(object), connection=NULL, ascii=FALSE)
  )
} # ser()

# Object to be serialized
key <- key0 <- list(abc="Hello");

# Store results
d <- list();

# 1. As is
d[[1]] <- ser(key);

# 2. Set names and redo (hardwired: identical to what's already there)
names(key) <- "abc";
d[[2]] <- ser(key);

# 3. Set names and redo (generic: char->raw->char)
key <- key0;
names(key) <- sapply(names(key), FUN=function(name)
rawToChar(charToRaw(name)));
d[[3]] <- ser(key);

# All names are identical
for (kk in 2:length(d))
  stopifnot(identical(d[[1]]$names, d[[kk]]$names));

# All raw names are identical
for (kk in 2:length(d))
  stopifnot(identical(d[[1]]$namesRaw, d[[kk]]$namesRaw));

# But, the serialized names differ.
print(identical(d[[1]]$ser, d[[2]]$ser));
print(identical(d[[1]]$ser, d[[3]]$ser));
print(identical(d[[2]]$ser, d[[3]]$ser));

So, it seems like there is some extra information in the names
attribute that is part of the serialization.  Is it possible to show
they differ at the R level?  What is that extra information?
Promises...?

Please enlighten me.

Henrik

Forgot...

On 8/31/07, Henrik Bengtsson <hb at stat.berkeley.edu>
wrote:
> Hi,
>
> I am puzzled with serialize().  It comes down generating identical
> hash codes for (apparently) identical objects using digest::digest(),
> which in turn relies on serialize().  Here is an example illustration
> the issue:
>
> ser <- function(object, ...) {
>   list(
>     names = names(object),
>     namesRaw = charToRaw(names(object)),
>     ser = serialize(names(object), connection=NULL, ascii=FALSE)
>   )
> } # ser()
>
> # Object to be serialized
> key <- key0 <- list(abc="Hello");
>
> # Store results
> d <- list();
>
> # 1. As is
> d[[1]] <- ser(key);
>
> # 2. Set names and redo (hardwired: identical to what's already there)
> names(key) <- "abc";
> d[[2]] <- ser(key);
>
> # 3. Set names and redo (generic: char->raw->char)
> key <- key0;
> names(key) <- sapply(names(key), FUN=function(name)
rawToChar(charToRaw(name)));
> d[[3]] <- ser(key);
>
> # All names are identical
> for (kk in 2:length(d))
>   stopifnot(identical(d[[1]]$names, d[[kk]]$names));
>
> # All raw names are identical
> for (kk in 2:length(d))
>   stopifnot(identical(d[[1]]$namesRaw, d[[kk]]$namesRaw));
>
> # But, the serialized names differ.
> print(identical(d[[1]]$ser, d[[2]]$ser));
> print(identical(d[[1]]$ser, d[[3]]$ser));
> print(identical(d[[2]]$ser, d[[3]]$ser));
With R version 2.6.0 Under development (unstable) (2007-08-23 r42614) I get:
[1] TRUE
[1] FALSE
[1] FALSE

and with R version 2.5.1 Patched (2007-07-19 r42284):
[1] FALSE
[1] FALSE
[1] TRUE
>
> So, it seems like there is some extra information in the names
> attribute that is part of the serialization.  Is it possible to show
> they differ at the R level?  What is that extra information?
> Promises...?
>
> Please enlighten me.
>
> Henrik
>