Initialising a new Dictionary with a List of keys

Question

I am initialising a new Dictionary and putting each key one by one like so:

igData = data.Select(x => new Dictionary<string, string> { ["Date"] = x.GetValueOrDefault("DATE"), ["SP"] = x.GetValueOrDefault("SP"), ["IG"] = x.GetValueOrDefault("IG")}).ToList();

This is fine but the rest of the keys need to be headers that I have created in List<string> headers

Is it possible to add this list of headers within the initialisation above? Something like this:

igData = data.Select(x => new Dictionary<string, string> { ["Date"] = x.GetValueOrDefault("DATE"), ["SP"] = x.GetValueOrDefault("SP"), ["IG"] = x.GetValueOrDefault("IG"), headers.Select(y => new KeyValuePair<string, string> (y, x.GetValueOrDefault["IG"])).ToList();

I understand the value is the same but that is intended. Is the above possible or is this something I would have separate. It would be ideal to do it in the above since I have access to the value from the data collection.

What is the type of data/headers? Why do you create so many dictionaries? — Cheng Chen
– Cheng Chen, Commented Jun 17, 2019 at 9:59
@ChengChen data is a List<Dictionary<string, string>> and headers is List<string>. — Usman Khan
– Usman Khan, Commented Jun 17, 2019 at 9:59
If you want a list of KeyValuePair<string, string>, then use List<KeyValuePair<string, string>> instead of a dictionary. You then have an option of using AddRange() to add multiple items at one time where a dictionary only has Add(). — jdweng
– jdweng, Commented Jun 17, 2019 at 10:06
A collection of dictionaries allways make me feel like -uaaah, yeah - uncconfortable. They tend to grow unexpectably and thus become less and less maintanable, in particular when you data-structures become more complex. Instead you should consider to create a class with the properties. — MakePeaceGreatAgain
– MakePeaceGreatAgain, Commented Jun 17, 2019 at 10:09

Jamiec · Accepted Answer · 2019-06-17 10:20:43Z

3

You cant do it in an initializer like that, but I'd suggest you can do it with a little bit of Concat and ToDictionary:

igData = data.Select(x => { return new KeyValuePair<string,string>[]{ new KeyValuePair<string,string>("Date", x.GetValueOrDefault("DATE")), new KeyValuePair<string,string>("SP", x.GetValueOrDefault("SP")), new KeyValuePair<string,string>("IG", x.GetValueOrDefault("IG")) }.Concat( headers.GetHalfHourlyTimeHeaders().Select(y => new KeyValuePair<string, string> (y, x.GetValueOrDefault["IG"])).ToList() ).ToDictionary(k => k.Key, v => v.Value); });

edited Jun 17, 2019 at 10:20

answered Jun 17, 2019 at 10:09

Jamiec

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5 Comments

Usman Khan Over a year ago

Is there a reason why you create an array of KVP instead of just initialising a new Dictionary and adding into that? Just trying to understand the code better.

Jamiec Over a year ago

Not really, just so I could chain (.Concat) them with your GetHalfHourlyTimeHeaders and create one dictionary.

Usman Khan Over a year ago

Oh okay, so adding straight into a Dictionary would not work with Concat?

Jamiec Over a year ago

It probably would, A Dictionary is just an IEnumerable<KeyValuePair<>> - the question is, is the overhead of another dictionary necessary.

Usman Khan Over a year ago

Okay, that makes sense. Thanks!

Cheng Chen · Accepted Answer · 2019-06-17 10:17:17Z

igData = data.Select(x => new Dictionary<string, string>(headers.GetHalfHourlyTimeHeaders().ToDictionary(y => y, y => x.GetValueOrDefault("IG"))) { ["Date"] = x.GetValueOrDefault("DATE"), ["SP"] = x.GetValueOrDefault("SP"), ["IG"] = x.GetValueOrDefault("IG") });

Query syntax looks better to me

igData = from x in data let ig = x.GetValueOrDefault("IG") select new Dictionary<string, string>(headers.GetHalfHourlyTimeHeaders().ToDictionary(y => y, y => ig)) { ["Date"] = x.GetValueOrDefault("DATE"), ["SP"] = x.GetValueOrDefault("SP"), ["IG"] = ig };

Joelius · Accepted Answer · 2019-06-17 10:19:21Z

Similar to the answer of Jamiec but in my opinion more readable (but not tested for performance):

List<Dictionary<string, string>> igData = data.Select(x => { var dict = new Dictionary<string, string> { ["Date"] = x.GetValueOrDefault("DATE"), ["SP"] = x.GetValueOrDefault("SP"), ["IG"] = x.GetValueOrDefault("IG") }; // I hope I understand correctly that GetHalfHourlyTimeHeaders returns List<string> foreach (string header in headers.GetHalfHourlyTimeHeaders()) { dict.Add(header, x.GetValueOrDefault("IG")); } return dict; } ).ToList();

Enigmativity · Accepted Answer · 2019-06-17 12:17:48Z

I like this way:

igData = data .Select(x => Enumerable .Concat( headers .GetHalfHourlyTimeHeaders() .Select(k => new { k, v = x.GetValueOrDefault("IG") }), new [] { "Date", "SP", "IG" } .Select(k => new { k, v = x.GetValueOrDefault(k.ToUpper()) })) .ToDictionary(z => z.k, z => z.v)) .ToList();

This doesn't work since it doesn't get the values from the data collection.
@UsmanKhan - Sorry, you're right. I missed that part of query. I've fixed it.

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