Build dictionary from array using Linq

Question

I have a class A containing an array of key/values pairs described by class B. One of the key is called "name". I want to use Linq to build a Dictionary<string, Dictionary<string, string>> where key of first dictionary is the attribute called "name" in the B array and the value is a second dictionary that contains the key/value pairs of B.

public class A
{
    public int a;
    public B[] b;
}

public class B
{
    public string key;
    public string value;
}

A[] a = new A[]
{
    new A { a = 1, b = new B[] { new B { key = "name", value = "n1"}, new B { key = "test", value = "t1" } }, },
    new A { a = 2, b = new B[] { new B { key = "name", value = "n2"}, new B { key = "test", value = "t2" } }, },
};

So in fact I would like to build the following dictionary using Linq on array "a":

Dictionary<string, Dictionary<string, string>> d = new Dictionary<string, Dictionary<string, string>>()
{
    { "n1",  new Dictionary<string, string>() { { "name", "n1" }, { "test", "t1" } } },
    { "n2",  new Dictionary<string, string>() { { "name", "n2" }, { "test", "t2" } } },
};

xanatos · Accepted Answer · 2017-04-05 06:39:40Z

2

It should be:

var dict = a.ToDictionary(
    x => x.b[0].value, 
    y => y.b.ToDictionary(z => z.key, z => z.value)
);

The only "fun" part of this LINQ expression is that I had to use up to z parameters (x, y, z)... It took me three compilations to get it right (I always name the parameters x)

Revised for comment:

var dict = a.ToDictionary(
    x => x.b.First(y => y.key == "name").value, 
    y => y.b.ToDictionary(z => z.key, z => z.value)
);

edited Apr 5, 2017 at 6:39

answered Apr 5, 2017 at 6:26

xanatos

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3 Comments

user957479 Over a year ago

Cool ! The parameter "name" may be randomly placed in the array (not necessarily the first element). How could I modify the expression to cope with this ?

xanatos Over a year ago

@user957479 Updated

user957479 Over a year ago

Thanks, it always looks so easy when you see the result ;-)

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