CODEWITHSUNDEEP
c#dictionary
Tony_KiloPapaMikeGolf
Tony_KiloPapaMikeGolf

Reputation: 889

Loading data from one Dictionary into another

I want to update data. From input data converted to same structure from one dictionary into another dictionary, my already existing data.

Pseudo code:

Dictionary<foo, bar> originalData; // Count = 128
Dictionary<foo, bar> inputData; // Count = 112

I could just write the following code:

foreach (var key in originalData.Keys)
{
    if (inputData.ContainsKey(key))
    {
        originalData[key] = inputData[key];
    }
}

But of course this will produce the following error:

"Collection was modified; enumeration operation may not execute."

What is the best way to handle this operation?

Upvotes: 1

Views: 110

Answers (3)

Sefe
Sefe

Reputation: 14017

Your problem is that you are modifying the collection you are iterating. You can use LINQ ToArray to iterate on a copy of your keys and avoid your problem:

foreach (var key in originalData.Keys.ToArray())
{
    if (inputData.ContainsKey(key))
    {
        originalData[key] = inputData[key];
    }
}

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 727077

You can start from the other end: rather than iterating originalData, iterate inputData:

foreach (var pair in inputData) {
    if (originalData.ContainsKey(pair.Key)) {
        originalData[pair.Key] = pair.Value;
    }
}

Note that by iterating key-value pairs you avoid the second look-up into inputData.

You can go further, and convert if to LINQ:

foreach (var pair in inputData.Where(p => originalData.ContainsKey(p.Key))) {
    originalData[pair.Key] = pair.Value;
}

Upvotes: 3

Patrick Hofman
Patrick Hofman

Reputation: 157136

Why not turn around the iterator? It is safe since you test the keys to exist in both dictionaries.

foreach (var key in inputData.Keys)
{
    if (originalData.ContainsKey(key))
    {
        originalData[key] = inputData[key];
    }
}

Upvotes: 3

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