Resolved Getting dictionary default value

[johnss]

I have a foreach loop like the following:

        private Dictionary<string,double> SumDictDaysExpDetail(Dictionary<int,Dictionary<string,string>> ddd)
        {
            Dictionary<string, double> dsum = appDataContext.MyFields.ToDictionary(l => l.drName, l => 0.0);

            foreach (string k in dsum.Keys)
            {
                List<string> ls = ddd.Select(l => l.Value.ContainsKey(k) ? l.Value[k] : "0,00").ToList();

                dsum[k] = ls.Sum(l => Convert.ToDouble(l));
            }

            return dsum;
        }

that I run with my dictionary ddd. I intend to calculate the sum for each header in a table, where the first int is the day of the month...
Now, when I run this loop I obtain a error saying that 'Collection was modified; enumeration operation may not execute.'.

But I don't alter the dictionary, at least consciously. When I use l.Value[k] ?? "0,00" gives also an error.

It seems that the use of .ContainsKey creates a key in the dictionary...

How may I do this?

 

[NoUserHere]

Don't modify a collection from within a loop.

This has been answered by myself if you search the forums.

 

[NoUserHere]

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csharpforums.net

 

[johnss]

Could you give me a link?

 

[Skydiver]

On line 5 you are iterating over the keys of the the dsum collection. Your line #9 is updating the dsum collection.

What you can do is change this:

foreach (string k in dsum.Keys)

to this:

foreach (string k in dsum.Keys.ToList())

to force getting a copy of all the keys before you start partying on the collection. Make sure this is truly you want to do, though.

 

[NoUserHere]

You have a link - I provided one on p/#3 which shows how to deal with it. As the problem you are reporting is the same one i addressed on that other topic.

What I linked you isn't much different to what Skydiver is tell you to do.

Do you understand why this is causing you problems?

 

[johnss]

Yes, I understand. I solved the problem with a copy of the keys as you both said.
However, I believe that the problem arises from line #8 because .ContainsKey somehow messes with the dictionary.
Thank you.

 

[NoUserHere]

The problem happens when the collection you iterate has one of its values changed while the collection is being navigated at the same time; you can't do that. And its not because you check a condition of the iteration itself, since checking a condition of any iteration won't cause a problem. You can not change a collection value while said collection is being cycled through.

And you're welcome.