Re: how to convert list to dictionary - C# Discussion Boards

31-Jul-09 3:55

List < string > lst = new List < string  > ();
     lst.Add("FirstValue");
     lst.Add("SecondValue");
     lst.Add("ThirdValue");
     lst.Add("FourthValue");

     // how do i convert lst to dictionary without using loop?

     Dictionary < string , int > dic = new Dictionary < string , int > ();
     // What type of parameter it will take??
     dic = lst.ToDictionary < string , int > ( ???? )

Henry Minute31-Jul-09 4:08

31-Jul-09 4:08

If you say why you want to do this and what the int value represents, it would be easier to advise you,

Henry Minute

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hotthoughtguy31-Jul-09 4:12

31-Jul-09 4:12

int is value of repeated string.
suppose lst.Add("this");
lst.Add("this");

Console.Write(dic["this"]) // will be 2 because of repeatation of "this".

hotthoughtguy31-Jul-09 4:14

Re: how to convert list to dictionary [modified]

31-Jul-09 4:14

this is known that same Key will throw exception but when key is repeated int is incremented and key will not register ( as it will throw exception)

Henry Minute31-Jul-09 5:06

31-Jul-09 5:06

try this:

public partial class ListToDictionaryTestForm : Form
{
    List<string> testList = new List<string>();

    public ListToDictionaryTestForm()
    {
        InitializeComponent();

        testList.Add("one");
        testList.Add("One");
        testList.Add("two");
        testList.Add("three");
        testList.Add("one");
        testList.Add("three");
        testList.Add("one");

        OutputResults(testList);
    }

    private void OutputResults(List<string> testList)
    {
        var itemcounts = from s in testList
                         group s by s into g
                         select new
                         {
                             key = g.Key,
                             val = g.Count()
                         };
        Dictionary<string, int> results = itemcounts.ToDictionary(k => k.key, v => v.val);

        foreach (KeyValuePair<string, int> kvp in results)
        {
            lboxResults.Items.Add(string.Format("{0} : {1}", kvp.Key, kvp.Value));
        }
    }
}

This is just a Form with a ListBox on it.

I've just realized that this can be abbreviated slightly:

private void OutputResults(List<string> testList)
{
    Dictionary<string, int> results = (from s in testList
                    group s by s into g
                    select new
                    {
                        key = g.Key,
                        val = g.Count()
                    }).ToDictionary(k => k.key, v => v.val);

    foreach (KeyValuePair<string, int> kvp in results)
    {
        lboxResults.Items.Add(string.Format("{0} : {1}", kvp.Key, kvp.Value));
    }
}

modified on Friday, July 31, 2009 11:38 AM

Luc Pattyn31-Jul-09 9:18

Luc Pattyn

31-Jul-09 9:18

However that doesn't satisfy the requirement "without using loop?"

you'll need stronger lambda magic, or an entirely different kind of Force!

Smile | :)

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Henry Minute31-Jul-09 9:22

31-Jul-09 9:22

Hey! Play fair. It only uses the loop, at least explicitly, to demonstrate that it has worked.

Luc Pattyn31-Jul-09 10:01

Luc Pattyn

31-Jul-09 10:01

as Dan points out below, there is a hidden loop in your magic, and as you said there is a visible one you don't need, so your solution actually contains two loops, that's way too much.

FWIW: The only way I see without loops is with recursion OMG | :OMG:

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Henry Minute31-Jul-09 10:11

31-Jul-09 10:11

Luc Pattyn wrote:
as Dan points out below, there is a hidden loop in your magic

That's why I explicitly said explicitly. Big Grin | :-D

Luc Pattyn wrote:
FWIW: The only way I see without loops is with recursion

Hadn't thought about that. You're probably correct, although isn't that a form of looping? In fact, isn't it a double loop? Once on the way through getting the results, and again whilst unwinding the recursion stack?

Luc Pattyn31-Jul-09 10:29

Luc Pattyn

31-Jul-09 10:29

Haven't seen a book yet that lists recursion as a loop construct; normally they only mention things such as for, while and do.

One must be careful, if the code is written in such a way that tail recursion is possible, then sooner or later (probably later) MS may come with a C# compiler that turns the recursive code into a loop, which to the OP (or his teacher?) would be unacceptable.

Going one step further, our computers execute loops all the time: fetch instruction, decode instruction, execute instruction; whether coded in micro-code or implemented in parallel hardware, each little piece is doing its job over and over. So maybe it can't be done? Or maybe yours is the solution they wanted...

Smile | :)

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Dan Neely31-Jul-09 9:26

Dan Neely

31-Jul-09 9:26

Luc Pattyn wrote:
you'll need stronger lambda magic,

You're still using a loop then, you're just applying a layer of obfuscation to hide it. Roll eyes | :rolleyes:

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Super Lloyd31-Jul-09 4:18

Super Lloyd

31-Jul-09 4:18

this is a bad question ya know?

what is supposed to go in the dictionary?

I can only make some guess....

first you can't avoid a loop, so here woud be one

Rand r = new Random();<br />
foreach(var s in lst) dic[rand.Netx()] = s;

but maybe we could use some LINQ magic to hide the loop?

Random r = new Random();<br />
Dictionary<int , string> dic = new Dictionary<int , string>();<br />
dic = lst.ToDictionary <string, int>(s => r.Next());

How about that?! Cool | :cool:

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_________________________________________________________
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hotthoughtguy31-Jul-09 4:28

31-Jul-09 4:28

StreamReader bfr = File.OpenText(@"D:\Documents and Settings\home\Desktop\normal.txt");
Dictionary < string , int > dic = new Dictionary < string , int > ();
string[] str = bfr.ReadToEnd().Replace("\r","").Replace("\n"," ").Replace(" "," ").Split(' ');
int var = 1;
foreach (string i in str)
{
if(dic.TryGetValue(i,out var))
dic[i]++;
else
dic.Add(i,1);
}
foreach(KeyValuePair < string , int > i in dic)
if(i.Value > 1)
Console.WriteLine(i.Key + " " + i.Value);
Console.ReadLine();

THIS WAS THE TASK BUT I HAVE DONE IT USING LOOP.
I WANT IT TO BE DONE without USING LOOP

0x3c031-Jul-09 4:38

0x3c0

31-Jul-09 4:38

If I understand your question correctly, you want a List<string> which looks like this:

Value1
Value2
Value3
Value4
Value1

to be converted to a Dictionary<string, int> which looks like this:

{Value1, 2}
{Value2, 1}
{Value3, 1}
{Value4, 1}

The problem is that the first argument of ToDictionary should provide a method to get the key from the value. You want to get the value from the key, so ToDictionary probably won't help you here. You could probably create a LINQ expression which provides a collection of KeyValuePair<string, int>, but IMHO it may not be worth it. It may be quicker to just bite the bullet and use a loop - ToDictionary does this behind the scenes anyway.

However, if you really dislike looping, then try something like this:

var keyValuePairs = from string key in lst.Distinct() select new KeyValuePair<string, int>(key,
    lst.Count(
        (string str) => (key == str))
    );

That should provide you with a list of KeyValuePairs. I'm not certain how to get those KeyValuePairs into a Dictionary, (maybe a cast or AddRange?) but it's a start.

Note: There may be syntax errors in that snippet; I wrote that in the browser, so the compiler hasn't done any error checking

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hotthoughtguy31-Jul-09 4:44

31-Jul-09 4:44

thankssssssssssssss
As you help people. God will help you..
Thanks again..