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06-26-2008
| #1 (permalink) |
| | something better than String.getHashCode On Jun 27, 7:12*am, "buu" <a...@xxxxxx> wrote: Quote: > You're right... > but, what if I want to check if some name & address exist, and by that > 'hash-key' there are some entries in dictionary wich are same by the key, > but not same by the content? you'll need a dictionary for each kind of key you want to look things up by. Jon |
My System Specs |
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06-26-2008
| #2 (permalink) |
| | Re: something better than String.getHashCode buu <aha@xxxxxx> wrote: Quote: > I'm using getHashCode sub from String object, but sometimes it gives me > duplicate values for different strings. Quote: > Difference is always when there are some numbers in strings. > > Is there any better/new getHash code function or any way to do some better > hashing? "source" values than "hash" values (as there clearly are in the case of strings hashing to any fixed size hash). If you want to use a hash for integrity checking etc you should use the classes derived from System.Security.Cryptography.HashAlgorithm - but if it's just for a hash table or similar structure, then GetHashCode should be absolutely fine. What's your actual use case? -- Jon Skeet - <skeet@xxxxxx> Web site: http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon_skeet C# in Depth: http://csharpindepth.com |
| My System Specs |
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06-26-2008
| #3 (permalink) |
| | Re: something better than String.getHashCode "Jon Skeet [C# MVP]" <skeet@xxxxxx> wrote in message news:MPG.22ce010d61403b4edc2@xxxxxx Quote: > buu <aha@xxxxxx> wrote: Quote: >> I'm using getHashCode sub from String object, but sometimes it gives me >> duplicate values for different strings. > Yes, it will. > Quote: >> Difference is always when there are some numbers in strings. >> >> Is there any better/new getHash code function or any way to do some >> better >> hashing? > Hashing will always give duplicate values when there are more potential > "source" values than "hash" values (as there clearly are in the case of > strings hashing to any fixed size hash). > > If you want to use a hash for integrity checking etc you should use the > classes derived from System.Security.Cryptography.HashAlgorithm - but > if it's just for a hash table or similar structure, then GetHashCode > should be absolutely fine. > > What's your actual use case? > > -- > Jon Skeet - <skeet@xxxxxx> > Web site: http://www.pobox.com/~skeet > Blog: http://www.msmvps.com/jon_skeet > C# in Depth: http://csharpindepth.com be best to search at the way to create a hashCode of that string and to use as a key in a dictionary. It's good, because it's fast, but it gives me duplicate hashCodes sometimes... |
| My System Specs |
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06-26-2008
| #4 (permalink) |
| | Re: something better than String.getHashCode buu <aha@xxxxxx> wrote: Quote: > I have a collection of Strings (names & addresses together) wich I found to > be best to search at the way to create a hashCode of that string and to use > as a key in a dictionary. > It's good, because it's fast, but it gives me duplicate hashCodes > sometimes... the whole point of dictionaries! The dictionary is going to take the hash code and use that itself (without assuming it's going to be unique) - why do you feel the need to take a hash yourself to start with? -- Jon Skeet - <skeet@xxxxxx> Web site: http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon_skeet C# in Depth: http://csharpindepth.com |
| My System Specs |
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06-27-2008
| #5 (permalink) |
| | Re: something better than String.getHashCode Buu, I don't know if you use this in a kind of batch process, otherwise remember that any interaction with a user will const much more time then you can win with any optimalizing of methods you describe now. A user will almost for sure not see the by you gained time by this. Cor "buu" <aha@xxxxxx> schreef in bericht news:1214511058.992007@xxxxxx Quote: > > "Jon Skeet [C# MVP]" <skeet@xxxxxx> wrote in message > news:MPG.22ce010d61403b4edc2@xxxxxx Quote: >> buu <aha@xxxxxx> wrote: Quote: >>> I'm using getHashCode sub from String object, but sometimes it gives me >>> duplicate values for different strings. >> Yes, it will. >> Quote: >>> Difference is always when there are some numbers in strings. >>> >>> Is there any better/new getHash code function or any way to do some >>> better >>> hashing? >> Hashing will always give duplicate values when there are more potential >> "source" values than "hash" values (as there clearly are in the case of >> strings hashing to any fixed size hash). >> >> If you want to use a hash for integrity checking etc you should use the >> classes derived from System.Security.Cryptography.HashAlgorithm - but >> if it's just for a hash table or similar structure, then GetHashCode >> should be absolutely fine. >> >> What's your actual use case? >> >> -- >> Jon Skeet - <skeet@xxxxxx> >> Web site: http://www.pobox.com/~skeet >> Blog: http://www.msmvps.com/jon_skeet >> C# in Depth: http://csharpindepth.com > I have a collection of Strings (names & addresses together) wich I found > to be best to search at the way to create a hashCode of that string and to > use as a key in a dictionary. > It's good, because it's fast, but it gives me duplicate hashCodes > sometimes... > > |
| My System Specs |
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06-27-2008
| #6 (permalink) |
| | Re: something better than String.getHashCode "Jon Skeet [C# MVP]" <skeet@xxxxxx> wrote in message news:MPG.22ce13419c129527dc4@xxxxxx Quote: > buu <aha@xxxxxx> wrote: Quote: >> I have a collection of Strings (names & addresses together) wich I found >> to >> be best to search at the way to create a hashCode of that string and to >> use >> as a key in a dictionary. >> It's good, because it's fast, but it gives me duplicate hashCodes >> sometimes... > You should use the string itself as the key in the dictionary. That's > the whole point of dictionaries! The dictionary is going to take the > hash code and use that itself (without assuming it's going to be > unique) - why do you feel the need to take a hash yourself to start > with? > > -- > Jon Skeet - <skeet@xxxxxx> > Web site: http://www.pobox.com/~skeet > Blog: http://www.msmvps.com/jon_skeet > C# in Depth: http://csharpindepth.com but, what if I want to check if some name & address exist, and by that 'hash-key' there are some entries in dictionary wich are same by the key, but not same by the content? |
| My System Specs |
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06-27-2008
| #7 (permalink) |
| | Re: something better than String.getHashCode On Jun 27, 7:12*am, "buu" <a...@xxxxxx> wrote: Quote: > You're right... > but, what if I want to check if some name & address exist, and by that > 'hash-key' there are some entries in dictionary wich are same by the key, > but not same by the content? you'll need a dictionary for each kind of key you want to look things up by. Jon |
| My System Specs |
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