There might be a good solution to the particular problem you're trying to solve, though. What are you trying to do?
On Friday, December 5, 2014 5:08:08 PM UTC-8, John Myles White wrote: > > For specialized cases it is possible to achieve 1-1-ness: > http://en.wikipedia.org/wiki/Perfect_hash_function > > But this is not something that most people aspire to do for most types > since 1-1-ness isn't essential in most applications and is costly to > achieve. > > -- John > > On Dec 5, 2014, at 5:03 PM, David Koslicki <[email protected] > <javascript:>> wrote: > > Ah, of course! I was hoping that on certain data types it was 1-1, but I > guess that was a long shot. Thanks for clarifying. > > On Friday, December 5, 2014 4:57:41 PM UTC-8, Jason Merrill wrote: >> >> If the space of possible hashes is smaller than the space of possible >> inputs (e.g. the hash is represented with fewer bits than the input data >> is), which is typically the case, then you can use the Pigeonhole Principle >> to prove what John wrote: >> >> https://en.wikipedia.org/wiki/Pigeonhole_principle >> >> On Friday, December 5, 2014 4:35:18 PM UTC-8, John Myles White wrote: >>> >>> This function is impossible to write in generality since hash functions >>> aren't one-to-one. >>> >>> -- John >>> >>> On Dec 5, 2014, at 4:32 PM, David Koslicki <[email protected]> wrote: >>> >>> > Hello, >>> > >>> > Is there a built in function that will undo hash()? >>> > >>> > i.e. I am looking for a function "dehash()" such that >>> > dehash(hash("ACTG")) == "ACTG" >>> > >>> > I can't seem to find this anywhere (documentation, google, this user >>> group, etc). >>> > >>> > Thanks, >>> > >>> > ~David >>> >>> >
