Convert Dictionary<stri ng,SomeType> keys to List<string>

[buzzweetman]

Many times I have a Dictionary<stri ng, SomeTypeand need to get the
list of keys out of it as a List<string>, to pass to a another method
that expects a List<string>.

I often do the following:

<BEGIN CODE>
List<stringkeyN ameList = new List<string>();

foreach (string keyName in this.myDictiona ry.Keys)
{
keyNameList.Add (keyName);
}

someObject.some Method(keyNameL ist);
<END CODE>

But it seems like there should be something built-in to give me a List
of the keys.
Am I missing something, or am I doing it the best way?

Thanks
Buzz

[Nicholas Paldino [.NET/C# MVP]]

Buzz,

You will want to do this:

// Get the list.
List<stringkeyN ameList = new List<string>(th is.myDictionary .Keys);

That will populate the list for you with the keys in the dictionary.

If your method is not going to modify the list, then you are better off
taking a parameter of IEnumerable<str ingand not List<string>. A list is
desirable when you have to make modifications to the list, but if you are
just iterating through the list, without having to make changes to the list
(but maybe to the members of the list), then IEnumerable<str ingis the
better choice.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

<bu*********@gm ail.comwrote in message
news:11******** **************@ b28g2000cwb.goo glegroups.com.. .

>
Many times I have a Dictionary<stri ng, SomeTypeand need to get the
list of keys out of it as a List<string>, to pass to a another method
that expects a List<string>.

I often do the following:

<BEGIN CODE>
List<stringkeyN ameList = new List<string>();

foreach (string keyName in this.myDictiona ry.Keys)
{
keyNameList.Add (keyName);
}

someObject.some Method(keyNameL ist);
<END CODE>

But it seems like there should be something built-in to give me a List
of the keys.
Am I missing something, or am I doing it the best way?

Thanks
Buzz

[buzzweetman]

Thank you Nicholas.
Great advice. I'll be using your IEnumerable tip also.

Buzz

Nicholas Paldino [.NET/C# MVP] wrote:

Buzz,

You will want to do this:

// Get the list.
List<stringkeyN ameList = new List<string>(th is.myDictionary .Keys);

That will populate the list for you with the keys in the dictionary.

If your method is not going to modify the list, then you are better off
taking a parameter of IEnumerable<str ingand not List<string>. A list is
desirable when you have to make modifications to the list, but if you are
just iterating through the list, without having to make changes to the list
(but maybe to the members of the list), then IEnumerable<str ingis the
better choice.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

<bu*********@gm ail.comwrote in message
news:11******** **************@ b28g2000cwb.goo glegroups.com.. .

Many times I have a Dictionary<stri ng, SomeTypeand need to get the
list of keys out of it as a List<string>, to pass to a another method
that expects a List<string>.

I often do the following:

<BEGIN CODE>
List<stringkeyN ameList = new List<string>();

foreach (string keyName in this.myDictiona ry.Keys)
{
keyNameList.Add (keyName);
}

someObject.some Method(keyNameL ist);
<END CODE>

But it seems like there should be something built-in to give me a List
of the keys.
Am I missing something, or am I doing it the best way?

Thanks
Buzz

[Larry Lard]

Nicholas Paldino [.NET/C# MVP] wrote:

Buzz,

You will want to do this:

// Get the list.
List<stringkeyN ameList = new List<string>(th is.myDictionary .Keys);

That will populate the list for you with the keys in the dictionary.

If your method is not going to modify the list, then you are better off
taking a parameter of IEnumerable<str ingand not List<string>. A list is
desirable when you have to make modifications to the list, but if you are
just iterating through the list, without having to make changes to the list
(but maybe to the members of the list), then IEnumerable<str ingis the
better choice.

If you just want an IEnumerable<K>, then Dictionary<K,V> .Keys is a
Dictionary.KeyC ollection<K>, which implements IEnumerable<Kal ready.

static void Main(string[] args)
{

Dictionary<stri ng, intdict = new Dictionary<stri ng, int>();

dict.Add("foo", 1);
dict.Add("bar", 2);
dict.Add("pop", 3);

ListStrings(dic t.Keys);

Console.ReadLin e();
}

static void ListStrings(IEn umerable<string list)
{
foreach (string s in list)
{
Console.WriteLi ne(s);
}
}
--
Larry Lard
la*******@googl email.com
The address is real, but unread - please reply to the group
For VB and C# questions - tell us which version

[buzzweetman]

I was passing List<stringbut now I've changed to IEnumerable<str ing>.
But now I hit a new ugliness...
I used to take that List and use the Contains method. Now with
IEnumerable I don;t have Contains. So it looks like I'll have to
foreach through... which seems kind of lame.

So it seems I DO want to pass a List<stringand just create the list
in the more elegant way that Nicholas suggsted in the first place:

// Get the list.
List<stringkeyN ameList = new List<string>(th is.myDictionary .Keys);

Unless there is yet more that I am missing.
Buzz

Larry Lard wrote:

Nicholas Paldino [.NET/C# MVP] wrote:

Buzz,

You will want to do this:

// Get the list.
List<stringkeyN ameList = new List<string>(th is.myDictionary .Keys);

That will populate the list for you with the keys in the dictionary.

If your method is not going to modify the list, then you are better off
taking a parameter of IEnumerable<str ingand not List<string>. A list is
desirable when you have to make modifications to the list, but if you are
just iterating through the list, without having to make changes to the list
(but maybe to the members of the list), then IEnumerable<str ingis the
better choice.

If you just want an IEnumerable<K>, then Dictionary<K,V> .Keys is a
Dictionary.KeyC ollection<K>, which implements IEnumerable<Kal ready.

static void Main(string[] args)
{

Dictionary<stri ng, intdict = new Dictionary<stri ng, int>();

dict.Add("foo", 1);
dict.Add("bar", 2);
dict.Add("pop", 3);

ListStrings(dic t.Keys);

Console.ReadLin e();
}

static void ListStrings(IEn umerable<string list)
{
foreach (string s in list)
{
Console.WriteLi ne(s);
}
}
--
Larry Lard
la*******@googl email.com
The address is real, but unread - please reply to the group
For VB and C# questions - tell us which version

[Marc Gravell]

If you want Contains, then ICollection<Tma y be the interface you want -
which Dictionary<TKey ,TValue>.KeyCol lection happens to implement...

Marc

[Larry Lard]

Marc Gravell wrote:

If you want Contains, then ICollection<Tma y be the interface you want -
which Dictionary<TKey ,TValue>.KeyCol lection happens to implement...

And if *all* we want to do is to see whether there is an entry with a
particular TKey, we just have to use Dictionary<,>.C ontainsKey!

I love System.Collecti ons.Generic!

--
Larry Lard
la*******@googl email.com
The address is real, but unread - please reply to the group
For VB and C# questions - tell us which version