How to build a look up table?

[Podi]

How to do this in C#?

I want to have a lookup table (hash) of city by zip code (integer) or
phone number (string), and it would look something like

x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"
x = book[10002]; // x == "Manhattan"
x = book["212-966-1234"]; // x == "Manhattan"

Thanks,
P

[Jon Shemitz]

Podi wrote:

How to do this in C#?

I want to have a lookup table (hash) of city by zip code (integer) or
phone number (string), and it would look something like

x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"
x = book[10002]; // x == "Manhattan"
x = book["212-966-1234"]; // x == "Manhattan"

There's a range of ways to do it.

A) book is a HashTable. You populate it like

book[94555] = "Fremont";
book["510-818-8888"] = "Fremont";

and you read it like

string x = (string) book[94555]; // x == "Fremont"
x = (string) book["510-818-8888"]; // x == "Fremont"

B) book is a Dictionary<stri ng, object>. You populate it like

book[94555] = "Fremont";
book["510-818-8888"] = "Fremont";

and you read it like

// no cast needed
string x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"

C) book is a Dictionary<Addr essKey, object>. You populate it like

book[new AddressKey(9455 5)] = "Fremont";
book[new AddressKey("510-818-8888")] = "Fremont";

and you read it like

string x = book[new AddressKey(9455 5)]; // x == "Fremont"
x = book[new AddressKey("510-818-8888")]; // x == "Fremont"

(C) involves a lot more code, and you'll be essentially duplicating
the same logic that (A) and (B) get for free - a boxed int is never
the same as a string and all that. It is possible, however, boxed
integers don't override Equals in an efficient way, that they do a
bytewise comparison, and AddressKey.Equa ls might be faster. I suppose
I should do some experiments, but I doubt that (C) will be noticeably
faster.

I'd go with (B), unless I had to stick to 1.1 still.

--

..NET 2.0 for Delphi Programmers
www.midnightbeach.com/.net
What you need to know.

[Dave Sexton]

Hi,

Create a business object to encapsulate the data:

class City
{
// use public properties instead
public int Zip;
public string Phone;
}

It depends on whether you want increased performance or less of a memory
footprint. There's a trade-off you'll have to make there. If you're using
the 2.0 framework and want a small memory footprint at the expense of
performance (although it shouldn't really matter anyway for relatively large
sets of data, depending on how frequently searches will be performed):

class CityList
: System.Collecti ons.ObjectModel .Collection<Cit y>
{
public new City this[int zip]
{
get
{
foreach (City city in this)
if (city.Zip == zip)
return city;

throw new KeyNotFoundExce ption(
"City not found with specified zip: " + zip);
}
}

public City this[string phone]
{
get
{
foreach (City city in this)
if (city.Phone == phone)
return city;

throw new KeyNotFoundExce ption(
"City not found with specified phone: " + phone);
}
}
}

If you want to increase performance (at the expense of memory) you can
maintain two sorted indexes (List<T>) within the CityList class itself and
implement IList explicitly instead of inheriting it from Collection<T>. One
List<Tinstance could be sorted by zip and the other by phone (call the
Sort method), and in each respective indexer you could call BinarySearch
instead of iterating over every item in the collection. Any operation
performed on one list must be performed on the other as well. e.g., Clear,
Add, Insert, Remove.

--
Dave Sexton

"Podi" <po*****@gmail. comwrote in message
news:11******** **************@ 80g2000cwy.goog legroups.com...

How to do this in C#?

I want to have a lookup table (hash) of city by zip code (integer) or
phone number (string), and it would look something like

x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"
x = book[10002]; // x == "Manhattan"
x = book["212-966-1234"]; // x == "Manhattan"

Thanks,
P

[Dave Sexton]

Hi Jon,

B) book is a Dictionary<stri ng, object>. You populate it like

I think you mean, Dictionary<obje ct, string:)

--
Dave Sexton

"Jon Shemitz" <jo*@midnightbe ach.comwrote in message
news:45******** *******@midnigh tbeach.com...

Podi wrote:

>How to do this in C#?

I want to have a lookup table (hash) of city by zip code (integer) or
phone number (string), and it would look something like

x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"
x = book[10002]; // x == "Manhattan"
x = book["212-966-1234"]; // x == "Manhattan"

There's a range of ways to do it.

A) book is a HashTable. You populate it like

book[94555] = "Fremont";
book["510-818-8888"] = "Fremont";

and you read it like

string x = (string) book[94555]; // x == "Fremont"
x = (string) book["510-818-8888"]; // x == "Fremont"

B) book is a Dictionary<stri ng, object>. You populate it like

book[94555] = "Fremont";
book["510-818-8888"] = "Fremont";

and you read it like

// no cast needed
string x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"

C) book is a Dictionary<Addr essKey, object>. You populate it like

book[new AddressKey(9455 5)] = "Fremont";
book[new AddressKey("510-818-8888")] = "Fremont";

and you read it like

string x = book[new AddressKey(9455 5)]; // x == "Fremont"
x = book[new AddressKey("510-818-8888")]; // x == "Fremont"

(C) involves a lot more code, and you'll be essentially duplicating
the same logic that (A) and (B) get for free - a boxed int is never
the same as a string and all that. It is possible, however, boxed
integers don't override Equals in an efficient way, that they do a
bytewise comparison, and AddressKey.Equa ls might be faster. I suppose
I should do some experiments, but I doubt that (C) will be noticeably
faster.

I'd go with (B), unless I had to stick to 1.1 still.

--

.NET 2.0 for Delphi Programmers
www.midnightbeach.com/.net
What you need to know.

[Dave Sexton]

Hi,

Actually, I like Jon's solutions better, although adding a business object
to encapsulate "City" might not be such a bad idea :)

--
Dave Sexton

"Dave Sexton" <dave@jwa[remove.this]online.comwrote in message
news:uS******** ******@TK2MSFTN GP03.phx.gbl...

Hi,

Create a business object to encapsulate the data:

class City
{
// use public properties instead
public int Zip;
public string Phone;
}

It depends on whether you want increased performance or less of a memory
footprint. There's a trade-off you'll have to make there. If you're
using the 2.0 framework and want a small memory footprint at the expense
of performance (although it shouldn't really matter anyway for relatively
large sets of data, depending on how frequently searches will be
performed):

class CityList
: System.Collecti ons.ObjectModel .Collection<Cit y>
{
public new City this[int zip]
{
get
{
foreach (City city in this)
if (city.Zip == zip)
return city;

throw new KeyNotFoundExce ption(
"City not found with specified zip: " + zip);
}
}

public City this[string phone]
{
get
{
foreach (City city in this)
if (city.Phone == phone)
return city;

throw new KeyNotFoundExce ption(
"City not found with specified phone: " + phone);
}
}
}

If you want to increase performance (at the expense of memory) you can
maintain two sorted indexes (List<T>) within the CityList class itself and
implement IList explicitly instead of inheriting it from Collection<T>.
One List<Tinstance could be sorted by zip and the other by phone (call
the Sort method), and in each respective indexer you could call
BinarySearch instead of iterating over every item in the collection. Any
operation performed on one list must be performed on the other as well.
e.g., Clear, Add, Insert, Remove.

--
Dave Sexton

"Podi" <po*****@gmail. comwrote in message
news:11******** **************@ 80g2000cwy.goog legroups.com...

>How to do this in C#?

I want to have a lookup table (hash) of city by zip code (integer) or
phone number (string), and it would look something like

x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"
x = book[10002]; // x == "Manhattan"
x = book["212-966-1234"]; // x == "Manhattan"

Thanks,
P

[Jon Shemitz]

Dave Sexton wrote:

B) book is a Dictionary<stri ng, object>. You populate it like

I think you mean, Dictionary<obje ct, string:)

Not again!

OK, time to volunteer for Soylent Green conversion.

--

..NET 2.0 for Delphi Programmers
www.midnightbeach.com/.net
What you need to know.

[Cor Ligthert [MVP]]

Prodi,

I like the often missed sortedlist for this.

http://msdn.microsoft.com/library/de...classtopic.asp

Cor

"Podi" <po*****@gmail. comschreef in bericht
news:11******** **************@ 80g2000cwy.goog legroups.com...

How to do this in C#?

I want to have a lookup table (hash) of city by zip code (integer) or
phone number (string), and it would look something like

x = book[94555]; // x == "Fremont"
x = book["510-818-8888"]; // x == "Fremont"
x = book[10002]; // x == "Manhattan"
x = book["212-966-1234"]; // x == "Manhattan"

Thanks,
P

[Podi]

Dave Sexton wrote:

Hi,

Actually, I like Jon's solutions better, although adding a business object
to encapsulate "City" might not be such a bad idea :)

Thanks to all for the suggestions.

The simple HashTable is nice and clean.

I now have some new requirements such as the look up table takes other
objects as keys. Two classes are added:

class Person
{ // Implementation details not shown
};

class Company
{ // Implementation details not shown
};

Person me = new Person();
Person myFriend = new Person();

Company csco = new Company();
Company intc = new Company();

// Is this possible? Preferrablly without change any existing code.
book[me] = "Milpitas";
book[myFriend] = "Sunnyvale" ;
book[csco] = "San Jose";
book[intc] = "Santa Clara";

[Jon Shemitz]

Podi wrote:

Thanks to all for the suggestions.

The simple HashTable is nice and clean.

Imho, the Dictionary<obje ct, stringis a lot cleaner - no need to
cast the result every time you read a value.

I now have some new requirements such as the look up table takes other
objects as keys. Two classes are added:

class Person
{ // Implementation details not shown
};

class Company
{ // Implementation details not shown
};

Person me = new Person();
Person myFriend = new Person();

Company csco = new Company();
Company intc = new Company();

// Is this possible? Preferrablly without change any existing code.
book[me] = "Milpitas";
book[myFriend] = "Sunnyvale" ;
book[csco] = "San Jose";
book[intc] = "Santa Clara";

Of course. Just be sure that the classes you use as keys override
GetHashCode and Equals.

--

..NET 2.0 for Delphi Programmers
www.midnightbeach.com/.net
What you need to know.

[Brian Gideon]

Cor,

You don't think a Hashtable or Dictionary<TKey , TValuewould be better
in this case?

Brian

Cor Ligthert [MVP] wrote:

Prodi,

I like the often missed sortedlist for this.

http://msdn.microsoft.com/library/de...classtopic.asp

Cor