Updating a collection using a lambda

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Paul Prewett - 07 Mar 2008 16:20 GMT

Hi -

I have a situation where I'd like to use a lambda, but I'm not sure how.
Basically, I have a collection of objects and I want to set a property on
each object that meets a condition.

Right now, I have this:

IEnumerable<VariableCode> codes =
variable.VariableCodeList.Where(c => c.Type == "MyCondition");
foreach (VariableCode code in codes)
{
code.IsShown = true;
}//foreach

I'm thinking that I can replace the foreach bit with a single lambda
expression. Can anyone help me with that syntax?

Thanks.

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-Paul Prewett

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Jon Skeet [C# MVP] - 07 Mar 2008 16:33 GMT

> I have a situation where I'd like to use a lambda, but I'm not sure how.
> Basically, I have a collection of objects and I want to set a property on
[quoted text clipped - 11 lines]
> I'm thinking that I can replace the foreach bit with a single lambda
> expression. Can anyone help me with that syntax?

Well, if you use List<T> instead, you can use List.ForEach.

Alternatively, you could (somewhat evilly) do:

var codes = from variable.VariableCodeList
where c.Type=="MyCondition"
select { c.IsShown=true; return c; } ;

(In other words, make the change part of the projection.)

Or you could write a ForEach extension method yourself - it would be
trivial to do.

Signature

Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk

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Paul Prewett - 07 Mar 2008 17:19 GMT

Hm, yes.

Well, VariableCodeList is actually a List<T>, but once I do the Where(), I
am stuck with IEnumerable<T>.

I'm thinking I'll just leave it the way that it is.

Thanks for the input, though.

Signature

-Paul Prewett

> > I have a situation where I'd like to use a lambda, but I'm not sure how.
> > Basically, I have a collection of objects and I want to set a property on
[quoted text clipped - 24 lines]
> Or you could write a ForEach extension method yourself - it would be
> trivial to do.

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Jon Skeet [C# MVP] - 07 Mar 2008 17:40 GMT

> Well, VariableCodeList is actually a List<T>, but once I do the Where(), I
> am stuck with IEnumerable<T>.

You can always call ToList() to get another List if you want.

Signature

Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk

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Paul Prewett - 07 Mar 2008 18:47 GMT

Ah. There we go.

Thankee, sai.

Signature

-Paul Prewett

> > Well, VariableCodeList is actually a List<T>, but once I do the Where(), I
> > am stuck with IEnumerable<T>.
>
> You can always call ToList() to get another List if you want.

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Updating a collection using a lambda

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