| Groups | Blog | Home |
dotnet faqs : Hash Tables
-Lou
Both.
A hash table is derived from the System.Collections namespace. This is from MSDN which is a good example on how to use one... The first value is the Key, the second is the Value. I'm not sure what you want to do so I gave a generic answer, but if you need something specific, let me know and I'll do what I can to help you. Cheers. Bill Hashtable phones = new Hashtable(); // Add items. phones.Add("John", "123-4567"); phones.Add("Enju", "351-8765"); phones.Add("Molly", "221-5678"); phones.Add("James", "010-4077"); phones.Add("Nelly", "110-5699"); phones.Add("Leah", "922-5699"); // Iterate through the collection. Console.WriteLine("Name\t\tNumber"); foreach (string name in phones.Keys) { Console.WriteLine(name +"\t"+ phones[name]); [quoted text, click to view] }"Lou" <lou.garvin@comcast.net> wrote in message news:er94Pt7cDHA.2564@TK2MSFTNGP09.phx.gbl... > is a Hash Table equivalent to a VB6 Collection or Dictionary object? > > -Lou > >
I need to use collections, like class collections and just some generic
collections and am not sure which is better, more efficiant etc. I noticed there are "Collections" "Dictionary" "Hash Table" and even some more. why so many collections? is there a reason to use one over another? Thanks... [quoted text, click to view] "William Ryan" <dotnetguru@nospam.comcast.net> wrote in message news:OcJPk0IdDHA.904@TK2MSFTNGP11.phx.gbl... > Both. > > A hash table is derived from the System.Collections namespace. This is from > MSDN which is a good example on how to use one... > The first value is the Key, the second is the Value. I'm not sure what you > want to do so I gave a generic answer, but if you need something specific, > let me know and I'll do what I can to help you. > > Cheers. > > Bill > Hashtable phones = new Hashtable(); > // Add items. > phones.Add("John", "123-4567"); > phones.Add("Enju", "351-8765"); > phones.Add("Molly", "221-5678"); > phones.Add("James", "010-4077"); > phones.Add("Nelly", "110-5699"); > phones.Add("Leah", "922-5699"); > > // Iterate through the collection. > Console.WriteLine("Name\t\tNumber"); > foreach (string name in phones.Keys) > { > Console.WriteLine(name +"\t"+ phones[name]); > }"Lou" <lou.garvin@comcast.net> wrote in message > news:er94Pt7cDHA.2564@TK2MSFTNGP09.phx.gbl... > > is a Hash Table equivalent to a VB6 Collection or Dictionary object? > > > > -Lou > > > > > >
Dictionary's and hashtables are collections. So are arraylists. Typically,
you'd use a collection and strongly type it so you enforce what it's members are. A hash Table for instace, allows you to effiiciently find members without having to iterate through them. ArrayLists for instance necessitate that you iterate through them to find a given member. Hash Tables don't let you iterate the same way. You could store whatever object in most of those structures...they are more alike then different. If You need to use collections, any of those will techincally meet the requirement. Think of it like this. If the boss said I need a Person to accomplish something, a Canadian, American or Mexican might be better suited to a task (for instance, a Mexican might be better at Spanish interpretation or languge specific task) but all three of the people are in fact 'Person's. So you would meet the requirement whichever you chose. [quoted text, click to view] "Lou" <lou.garvin@comcast.net> wrote in message news:uI5tiyhdDHA.728@TK2MSFTNGP11.phx.gbl... > I need to use collections, like class collections and just some generic > collections and am > not sure which is better, more efficiant etc. I noticed there are > "Collections" > "Dictionary" > "Hash Table" > and even some more. > > why so many collections? > is there a reason to use one over another? > > Thanks... > > "William Ryan" <dotnetguru@nospam.comcast.net> wrote in message > news:OcJPk0IdDHA.904@TK2MSFTNGP11.phx.gbl... > > Both. > > > > A hash table is derived from the System.Collections namespace. This is > from > > MSDN which is a good example on how to use one... > > The first value is the Key, the second is the Value. I'm not sure what > you > > want to do so I gave a generic answer, but if you need something > specific, > > let me know and I'll do what I can to help you. > > > > Cheers. > > > > Bill > > Hashtable phones = new Hashtable(); > > // Add items. > > phones.Add("John", "123-4567"); > > phones.Add("Enju", "351-8765"); > > phones.Add("Molly", "221-5678"); > > phones.Add("James", "010-4077"); > > phones.Add("Nelly", "110-5699"); > > phones.Add("Leah", "922-5699"); > > > > // Iterate through the collection. > > Console.WriteLine("Name\t\tNumber"); > > foreach (string name in phones.Keys) > > { > > Console.WriteLine(name +"\t"+ phones[name]); > > }"Lou" <lou.garvin@comcast.net> wrote in message > > news:er94Pt7cDHA.2564@TK2MSFTNGP09.phx.gbl... > > > is a Hash Table equivalent to a VB6 Collection or Dictionary object? > > > > > > -Lou > > > > > > > > > > > >
Thanks William, that was well said. You'd make a great teacher.
-Lou [quoted text, click to view] "William Ryan" <dotnetguru@nospam.comcast.net> wrote in message news:e0SHbp%23dDHA.620@TK2MSFTNGP11.phx.gbl... > Dictionary's and hashtables are collections. So are arraylists. Typically, > you'd use a collection and strongly type it so you enforce what it's members > are. A hash Table for instace, allows you to effiiciently find members > without having to iterate through them. ArrayLists for instance necessitate > that you iterate through them to find a given member. Hash Tables don't let > you iterate the same way. You could store whatever object in most of those > structures...they are more alike then different. > > If You need to use collections, any of those will techincally meet the > requirement. Think of it like this. If the boss said I need a Person to > accomplish something, a Canadian, American or Mexican might be better suited > to a task (for instance, a Mexican might be better at Spanish interpretation > or languge specific task) but all three of the people are in fact 'Person's. > So you would meet the requirement whichever you chose. > "Lou" <lou.garvin@comcast.net> wrote in message > news:uI5tiyhdDHA.728@TK2MSFTNGP11.phx.gbl... > > I need to use collections, like class collections and just some generic > > collections and am > > not sure which is better, more efficiant etc. I noticed there are > > "Collections" > > "Dictionary" > > "Hash Table" > > and even some more. > > > > why so many collections? > > is there a reason to use one over another? > > > > Thanks... > > > > "William Ryan" <dotnetguru@nospam.comcast.net> wrote in message > > news:OcJPk0IdDHA.904@TK2MSFTNGP11.phx.gbl... > > > Both. > > > > > > A hash table is derived from the System.Collections namespace. This is > > from > > > MSDN which is a good example on how to use one... > > > The first value is the Key, the second is the Value. I'm not sure what > > you > > > want to do so I gave a generic answer, but if you need something > > specific, > > > let me know and I'll do what I can to help you. > > > > > > Cheers. > > > > > > Bill > > > Hashtable phones = new Hashtable(); > > > // Add items. > > > phones.Add("John", "123-4567"); > > > phones.Add("Enju", "351-8765"); > > > phones.Add("Molly", "221-5678"); > > > phones.Add("James", "010-4077"); > > > phones.Add("Nelly", "110-5699"); > > > phones.Add("Leah", "922-5699"); > > > > > > // Iterate through the collection. > > > Console.WriteLine("Name\t\tNumber"); > > > foreach (string name in phones.Keys) > > > { > > > Console.WriteLine(name +"\t"+ phones[name]); > > > }"Lou" <lou.garvin@comcast.net> wrote in message > > > news:er94Pt7cDHA.2564@TK2MSFTNGP09.phx.gbl... > > > > is a Hash Table equivalent to a VB6 Collection or Dictionary object? > > > > > > > > -Lou > > > > > > > > > > > > > > > > > > > >
[quoted text, click to view]
Lou wrote: > I need to use collections, like class collections and just some > generic collections and am > not sure which is better, more efficiant etc. I noticed there are > "Collections" > "Dictionary" > "Hash Table" > and even some more. > > why so many collections? > is there a reason to use one over another? > There are several criteria. The most important is how you will access the data in the collection. Do you want serial access to read data (ie start at the first item, then the second, then the third, etc) or do you want random access (ie read item 13, read item 5, read item 22, etc)? When you write data to the collection will you write them in the order that they will be read (a Queue is good for this) or do you know the exact position that you want the item in the collection (ie write item 13, then item 44 etc)? A class that supports IEnumerable is designed to allow serial access so that you repeatedly read a value from the collection until the end is reached. A class that supports ICollection has the IEnumerable features as well as a Count to determine the number of items in the collection. IDictionary means that items can be accessed by some index object that you specify as a key (for example the SSN is a key for a Hashtable of employee names). A class with IList means that the collection has ransom access using the position of the item as the index. Do you know the size of the collection when you create it, or do you want the collection to grow as more items are inserted? Do you want to rearrange the order of the items after you have inserted them into the collection? Do you want to do a search for an item with a specific value? Finally, what type item will be in the collection - will they be the same type (eg all strings) or will you put different types of items in the collection? If you want to create an array of value types (eg integers or real numbers) then it is better to use an array because the items will be 'boxed' when they are put in the collection which means that a new object is created for each item and this will increase your memory usage (and there are other issues with boxing). - Array is fixed size, allows random access and allows searches and reordering. An array is typed. - ArrayList is variable size, allows randowm access, searching and reordering and is untyped. It can be used to create an array from the items in the collection. - Hashtable is not ordered by the order that you inserted the items, it is variable size, allows random access. The time taken to get an item in a Hashtable is only as good as the hash. - SortedList contain key-value pairs, sorted according to the key, hence inserting items takes time. Supports searches by key or value. Richard -- my email evpuneqt@zicf.bet is encrypted with ROT13 (www.rot13.org)
Don't see what you're looking for? Try a search.
|
June 2003
July 2003
August 2003
September 2003
October 2003
November 2003
December 2003
January 2004
February 2004
March 2004
April 2004
May 2004
June 2004
July 2004
August 2004
September 2004
October 2004
November 2004
December 2004
January 2005
February 2005
March 2005
April 2005
May 2005
June 2005
July 2005
August 2005
September 2005
October 2005
November 2005
December 2005
January 2006
February 2006
March 2006
April 2006
May 2006
June 2006
July 2006
August 2006
September 2006
October 2006
November 2006
December 2006
January 2007
February 2007
March 2007
April 2007
May 2007
June 2007
July 2007
August 2007
September 2007
October 2007
November 2007
December 2007
January 2008
February 2008
March 2008
April 2008
May 2008
June 2008
| home · blog · groups | Questions? Comments? Contact the dn |