Yeah, I could see Key ordering or Entry ordering both make sense
depending on the context :)
Adam J. Shook wrote:
I personally think all maps with the same keys should be sorted
together, but I think it'd be best to support and document both ways and
leave that up to the user. I'm sure either way could be argued, and
this is certainly an edge case for lexicoders.
On Tue, Dec 29, 2015 at 7:16 PM, Keith Turner <[email protected]
<mailto:[email protected]>> wrote:
Do you want all maps with the same keys to sort together? If so
doing abc123 would make that happen.
The map data below
{ a : 1 , b : 2, c : 3 }
{ a : 1 , x : 8, y : 9 }
{ a : 4 , b : 5, c : 6 }
Would sort like the following if encoding key values pairs
a1b2c3
a1x8y9
a4b5c6
If encoding all key and then all values, it would sort as follows
abc123
abc456
axy189
On Tue, Dec 29, 2015 at 4:53 PM, Adam J. Shook <[email protected]
<mailto:[email protected]>> wrote:
Agreed, I came to the same conclusion while implementing. The
final result that I have is a SortedMapLexicoder to avoid any
comparisons going haywire. Additionally, would it be best to
encode the map as an array of keys followed by an array of
values, or encode all key value pairs back-to-back:
{ a : 1 , b : 2, c : 3 } encoded as
a1b2c3
-or-
abc123
Feels like I should be encoding a list of keys, then the list of
values, and then concatenating these two encoded byte arrays. I
think the end solution will be to support both? I'm having a
hard time reconciling which method is better, if any. Hard to
find some good examples of people who are sorting a list of maps.
On Tue, Dec 29, 2015 at 2:47 PM, Keith Turner <[email protected]
<mailto:[email protected]>> wrote:
On Mon, Dec 28, 2015 at 11:47 AM, Adam J. Shook
<[email protected] <mailto:[email protected]>> wrote:
Hello all,
Any suggestions for using a Map Lexicoder (or
implementing one)? I am currently using a new
ListLexicoder(new PairLexicoder(some lexicoder, some
lexicoder), which is working for single maps. However,
when one of the lexicoders in the Pair is itself a Map
(and therefore another ListLexicoder(PairLexicoder)), an
exception is being thrown because ArrayList is not
Comparable.
Since maps do not have a well defined order of keys and
values, comparison is tricky. The purpose of Lexicoders is
encode things in such a way that the lexicographical
comparison of the serialized data is possible. With a
hashmap if I add the same data in the same order to two
different hash map instances, its possible that when
iterating over those maps I could see the data in different
orders. This could lead to two maps constructed in the
same way at different times (like different JVMs with
different implementations of HashMap) generating different
data that compare as different. Ideally comparison of the
two would yield equality.
Something like LinkedHashMap does not have this problem for
the same insertion order. If you want things to be
comparable regardless of insertion order (which I think is
more intuitive), then SortedMap seems like it would be a
good candidate. So maybe a SortedMapLexicoder would be a
better thing to offer?
Regards,
--Adam
