Hi,
I need a way to reduce a compound value, say {:foo "bar"}, into a number
(like 693d9a0698aff95c in hex). I don't necessarily need a very large hash
space, 7 hex digits is good enough for my purposes. But I need
this hash to be consistent between runs and JVM versions etc. So I guess
that rules out standard object hashes.
I would like to find a sufficiently fast way to do this. I can live with
MD5, but are there faster alternatives (but produce smaller hashes)? (
clj-digest <https://github.com/tebeka/clj-digest> provides a nice interface
to what Java provides but there are only usual suspects AFAICS
<http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#MessageDigest>
)
I will be dealing with unordered collections, but it seems hashing is
consistent when the input order is changed:
user=> (.hashCode {:foo "Bar" :baz 5})
2040536238
user=> (.hashCode {:baz 5 :foo "Bar"})
2040536238
(It even gave the same hash code in different runs.)
I will use these hashes to build index tables. My data, that contains these
things I hash is a set. I will store this as an ordered set and keep an
index pointing to where records from this hash to that hash lives. This is
all Clojure, but I can't keep all my data in memory. (So Clojure's
persistent data structures is out of the picture. life would've been much
simpler if I could.)
Thanks for reading. Any insight is appreciated.
--
Kind Regards,
Atamert Ölçgen
◻◼◻
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www.muhuk.com
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