Type conversion for dictionaries with list value in C#-CodePudding

What is the best way to convert from Dictionary<double, List<double>> to Dictionary<double, List<double?>>? Here are the steps I have taken so far:

1-For List<double> to List<double?>, the following works (not sure if it is the most effiecient way): List<double?> newDic = oldDic.Select(s => (double?) s).ToList();

2- And for the Dictionary converstion, I have tried: Dictionary <double, List<double?>> newDic = oldDic.Keys.Select(key => new { Key = key, Value = new List<double?>() { oldDic[key].Select(s => (double?) s).ToList()} }).ToDictionary(grp => grp.Key, grp => grp.Value); This does not work and I do not know how to make it work. I appreciate any comments.

CodePudding user response：

You can call ToDictionary directly. There is no need to create the intermediate anonymous type:

oldDict.ToDictionary(
    x => x.Key, // x here is already a KeyValuePair<double, List<double>>
    // you already know how to convert a List<double> to List<double?>,
    // do it to x.Value here: 
    x => x.Value.Select(y => (double?)y).ToList()
)