C# Lambda-Select with conditions

Question

I created a Command-class which has two important members.

public class Command
{
    public string Name { get; set; }
    public CommandExecutedCallback Callback { get; set; }
    public delegate void CommandExecutedCallback(Command command);
}

I save multiple objects of this class in a List<Command>.

Another class CommandProcessor has a member function GetCallbacks(string name).

I want to use a lambda expression to get an array of CommandExecutedCallback-delegates with the condition that the name matches.

I can get all Callbacks with: return commandList.Select(t => t.Callback).ToArray().

How can i insert the condition to get only commands with the specified name?

Thank you in advance.

Select is for a projection. Use Where for filtering.

Jon Skeet
– Jon Skeet

2016-03-29 17:08:32 +00:00
Commented Mar 29, 2016 at 17:08 — Jon Skeet
– Jon Skeet, Commented Mar 29, 2016 at 17:08

Jason Watkins · Accepted Answer · 2016-03-29 17:08:42Z

11

You need to a add a Where condition:

return commandList.Where(t => t.Name == name).Select(t => t.Callback);

You should also avoid calling ToArray unless you really need to. Unless you're specifically passing this data to some other method that requires an array, copying all of the data with ToArray is probably an unnecessary (and rather expensive) operation.

answered Mar 29, 2016 at 17:08

Jason Watkins

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1 Comment

Johannes Jacobs Over a year ago

This is exactly what i was looking for. Thank you so much.

DLeh · Accepted Answer · 2016-03-29 17:08:24Z

2

Is this what you mean?

return commandList
    .Where(t => t.Name == "someName")
    .Select(t => t.Callback)
    .ToArray();

answered Mar 29, 2016 at 17:08

DLeh

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1 Comment

Johannes Jacobs Over a year ago

Also, this is what i was looking for. Thank you too :)

Luis Tellez · Accepted Answer · 2016-03-29 17:17:03Z

0

You need to use the WHERE not the SELECT. With Select you tell what you wnat from the list, and with WHERE you filter the list to show.

return commandList.Where(t => t.Name == "VALUE").Select(t => t.Callback)

edited Mar 29, 2016 at 17:17

answered Mar 29, 2016 at 17:08

Luis Tellez

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2 Comments

Jason Watkins Over a year ago

You dropped the Select, which is still necessary.

Luis Tellez Over a year ago

I changed it, but I think its more important if he understand the difference between both of them.

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