Re: reverse lookup in dictionary - C# Discussion Boards

4-Aug-08 1:45

Is there any data structure avilable out of the box in Framework 3.5, kind of reverse lookup dictionary.

Dictionary< key1, key2 > d = new Dictionary< key1, key2>();
 Key2  k2 = d[key1];   // normal
 Key1  k1 =  d[key2];  // specify the key2 and get key1 -- needed

Thanks

Regards,
Vythees

Miles to go before sleep...

User 66584-Aug-08 2:12

User 6658

4-Aug-08 2:12

There is no reverse lookup in a dictionary because one value can lead to multiple keys, but not the other way round.

To get a list of keys that result in a specific value you can use this:

var keys = from key in dic.Keys
		where dic[key] == somevalue
		select key;

regards

modified 12-Sep-18 21:01pm.

vytheese4-Aug-08 2:19

4-Aug-08 2:19

Thanks,

but in my case both are unique.

Regards,
Vythees

Miles to go before sleep...

User 66584-Aug-08 2:25

User 6658

4-Aug-08 2:25

vytheese wrote:
but in my case both are unique.

In this case I would derive a class from IDictionary that will internally hold two dictionaries, one for key->value and one for value->key. Something like:

public class TwoWayDictionary<K, V> : IDictionary<K, V>

Override the methods like Add, Contains etc to allow adding, removing and searching by key and value in both of the dictionaries.

regards

modified 12-Sep-18 21:01pm.

vytheese4-Aug-08 2:41

4-Aug-08 2:41

The wrapper will ease from access point of view but Again I will end up in performance issue while searching from value point.

Regards,
Vythees

Miles to go before sleep...

Unscrambling Eggs: Decompiling ASP.NET

Brady Kelly4-Aug-08 2:45

Brady Kelly

4-Aug-08 2:45

Why? You will be looking up the value as a key in your second dictionary.

vytheese4-Aug-08 3:00

4-Aug-08 3:00

Good, Sorry I failed to notice that. But in any case its only a wrapper for me.

What I am looking for is single dictionary with key, values both indexed or hashed.

since in my scenario the collection I am expecting is huge and time for process is having little window. so I want to get the feasible data structure that will helps me in both (space/time).

But with the time contstraint for my execution I have to trade between space vs time for a intial release.

Grazie.

Regards,
Vythees

Miles to go before sleep...

leppie4-Aug-08 3:24

leppie

4-Aug-08 3:24

vytheese wrote:
What I am looking for is single dictionary with key, values both indexed or hashed.

That exactly what a wrapper class with 2 dictionaries will do...

xacc.ide - now with TabsToSpaces support
IronScheme - 1.0 alpha 4a out now (29 May 2008)

.Tex files and word equations

PIEBALDconsult4-Aug-08 13:53

PIEBALDconsult

4-Aug-08 13:53

Yeah, I just use two Dictionaries.

chrisha844-Aug-08 1:18

chrisha84

4-Aug-08 1:18

hi,

can anybody give me a tip (may be a little tip) to create word equations using .tex files automatically.

thanks in advance.

why we use CaspolSecurityPolicyCreator.cs Class

wasimsharp4-Aug-08 1:16

wasimsharp

4-Aug-08 1:16

My Boss give me a project and say read it Compleatly in this Project there is Class Called CaspolSecurityPolicyCreator.cs i serach it on net but did not Found any help can any body tell me why we use it. The Project is Of add-on on Outlook

wasim khan

Re: why we use CaspolSecurityPolicyCreator.cs Class

Ashfield4-Aug-08 1:31

Ashfield

4-Aug-08 1:31

Well, I suspect if you didn't find it on the net it must be something written by or bought by your company. try asking some of your colleagues.

Bob
Ashfield Consultants Ltd

Silly question - bool initialization in C#

Mohammad A Gdeisat4-Aug-08 1:03

4-Aug-08 1:03

Although I've been programming for years but I need somebody to explicitly assure me that I am correct as I am developing a critical piece of software. The problem is that when you need a very basic rule you cannot find it on search engines Smile | :)

when I define a variable of bool like this:

bool b;

is it automatically initialized to false?

what about int? is it automatically initialized to zero?

Thanks all Big Grin | :-D

And ever has it been that love knows not its own depth until the hour of separation

Mohammad Gdeisat

wasimsharp4-Aug-08 1:13

wasimsharp

4-Aug-08 1:13

i think that u have a lot of time thats why u write this message please check it by ur self creating one boool variable and int.

wasim khan

Mohammad A Gdeisat4-Aug-08 1:16

4-Aug-08 1:16

Well, if I use your genius method then I'll have a 50% possibility of getting a wrong answer, plus consider that I am writing a critical piece of code, not a game - Thanks anyway

And ever has it been that love knows not its own depth until the hour of separation

Mohammad Gdeisat

MarkB7774-Aug-08 1:48

MarkB777

4-Aug-08 1:48

Mohammad A Gdeisat wrote:
I am writing a critical piece of code, not a game

Tell that to the lead designer of an upcoming game title.

Mark Brock

Click here to view my blog

Mohammad A Gdeisat4-Aug-08 1:50

4-Aug-08 1:50

hahahaha

you are 100% right, my expression was definitely wrong Smile | :)

I mean it is not a game (i.e. I am not playing around with this code), thats what I meant. Smile | :)

good joke

And ever has it been that love knows not its own depth until the hour of separation

Mohammad Gdeisat

J4amieC4-Aug-08 2:20

J4amieC

4-Aug-08 2:20

Mohammad A Gdeisat wrote:
Well, if I use your genius method then I'll have a 50% possibility of getting a wrong answer

How do you come to this conclusion?

if you wrote the following code it would 100% give you the answer to your question:

bool testBool;
Console.WriteLine(testBool); // output: false
int testInt;
Console.WriteLine(testInt); // output: 0

Mohammad A Gdeisat4-Aug-08 5:28

4-Aug-08 5:28

1st, I was talking about bool which was the main concern.

2nd, it is 100% for u becoz u already know it.

Anyway, let's end here.

And ever has it been that love knows not its own depth until the hour of separation

Mohammad Gdeisat

Simon P Stevens4-Aug-08 1:13

Simon P Stevens

4-Aug-08 1:13

Yes bool defaults to false and int defaults to 0 if it's a class member variable. I think FxCop/VS code analysis gives warnings if you do try to initialise it, and suggests that it's not necessary.

If it's a private local variable, the compiler won't yet you use it without explicitly initialising it to something. You'll get a "Use of anassigned local variable 'x' error.

Simon

Mohammad A Gdeisat4-Aug-08 1:17

4-Aug-08 1:17

Thanks for the detailed answer mate, I bet most of us don't know the details Smile | :)

And ever has it been that love knows not its own depth until the hour of separation

Mohammad Gdeisat

User 66584-Aug-08 1:15

User 6658

4-Aug-08 1:15

bool: false
int: 0

You can find more information in the C# language specification[^], section 5.2 Default values and especially section 4.1.2 Default constructors:

For all simple-types, the default value is the value produced by a bit pattern of all zeros:
For sbyte, byte, short, ushort, int, uint, long, and ulong, the default value is 0.
For char, the default value is '\x0000'.
For float, the default value is 0.0f.
For double, the default value is 0.0d.
For decimal, the default value is 0.0m.
For bool, the default value is false.

regards

modified 12-Sep-18 21:01pm.

Mohammad A Gdeisat4-Aug-08 1:17

4-Aug-08 1:17

Thank you mate Wink | ;)

And ever has it been that love knows not its own depth until the hour of separation

Mohammad Gdeisat