CODEWITHSUNDEEP
c#.net
Nate222
Nate222

Reputation: 886

Convert List to Dictionary<string, string[]>

I have a simple custom object:

class CertQuestion
{
    public string Field {get;set;}
    public string Value {get;set;}
}

Subsequently I find myself with a List in some code. I'm trying to figure out how to format a list of CertQuestions into a corresponding Dictionary with similar Field names grouped together. For instance, given the following list:

        List<CertQuestion> certQuestions = new List<CertQuestion>()
            {
                new CertQuestion("Key", "Value1"),
                new CertQuestion("Key", "Value2"),
                new CertQuestion("Key2", "Value"),
                new CertQuestion("Key2", "Value2")
            };

I would like to convert that (trying to use LINQ) into a Dictionary with two entries such as 

{{"Key", "Value1, Value2"}, {"Key2", "Value, Value2"}}

Upvotes: 1

Views: 9311

Answers (2)

rclement
rclement

Reputation: 1714

Group the questions by field, then convert to dictionary by selecting key, then value. Value becomes the grouping's list.

certQuestions.GroupBy(c => c.Field)
             .ToDictionary(k => k.Key, v => v.Select(f => f.Value).ToList())

Or for an array:

certQuestions.GroupBy(c => c.Field)
             .ToDictionary(k => k.Key, v => v.Select(f => f.Value).ToArray())

Edit based on question in comment:

class CertTest 
{
    public string TestId {get;set;}
    public List<CertQuestion> Questions {get;set;}
}
var certTests = new List<CertTest>();

You would use the SelectMany extension method. It is designed to aggregate a property list object that is in each element of the original list: 

certTests.SelectMany(t => t.Questions)
         .GroupBy(c => c.Field)
         .ToDictionary(k => k.Key, v => v.Select(f => f.Value).ToList())

Upvotes: 13

Jamiec
Jamiec

Reputation: 136074

Your requirement was for a comma-separated list of values, that can be done like this:

var dict = certQuestions.GroupBy(c => c.Field)
             .ToDictionary(k => k.Key, v => String.Join(", ", v.Select(x => x.Value)))

Live example: http://rextester.com/LXS58744

(You should consider whether what you actually want is the values to be an Array or List<string> - see other answers)

Upvotes: 3

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