C# How to declare new Dictionary object based off a string array within a LINQ query

Question

I have some code like this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

class Program
{
    static void Main(string[] args)
    {
        string xml = @"<Root>
  <Report1>
    <Row>
      <Field1>data1-1</Field1>
      <Field2>data1-2</Field2>
      <!-- many more fields -->
    </Row>
    <Row>
      <Field1>data2-1</Field1>
      <Field2>data2-2</Field2>
      <!-- many more fields -->
    </Row>
  </Report1>
</Root>";

        XDocument doc = XDocument.Parse(xml);

        var report1 = from report in doc.Root.Elements("Report1").Elements("Row")
                      select new Dictionary<string, string>()
                          {
                              {"Field1", report.Elements("Field1").First().Value},
                              {"Field2", report.Elements("Field2").First().Value}
                          };

        var i = 1;
        foreach (Dictionary<string, string> dict in report1)
        {
            Console.WriteLine(String.Format("Row{0}: ", i));
            Console.WriteLine("  Field1: {0}", dict["Field1"]);
            Console.WriteLine("  Field2: {0}", dict["Field2"]);
            i++;
        }

        Console.ReadLine();
    }
}

Would it be possible to define a string array or some other data structure that I could use to declare these dictionary objects? Here is some silly pseudo code help show my idea:

EDIT The variable fieldNames in the pseudo code below would be an array of names I expect, not based on the xml source field names. I will be ignoring any field names within the xml source that are not explicitly set in the fieldNames array.

var report1 = from report in doc.Root.Elements("Report1").Elements("Row")
              select new Dictionary<string, string>()
           {
              foreach (var fieldName in fieldNames)
              {
                  {fieldName, report.Elements(fieldName).First().Value}
              }
           };

even after the edit it still isn't entirely obvious whether the set of fields you want in the report is based on the xml contents or not. — Tar
– Tar, Commented Nov 8, 2012 at 19:57
@Tar, thanks I made an edit. The fields I want to import are not based on the xml source, it would be what is explicitly set in the array or list. — programmer
– programmer, Commented Nov 8, 2012 at 20:08

Thom Smith · Accepted Answer · 2012-11-08 19:43:51Z

5

Use Enumerable.ToDictionary:

var report1 = 
    from report in doc.Root.Elements("Report1").Elements("Row")
    select new[] {"Field1", "Field2", "Field3"}
        .ToDictionary(x => x, x => report.Elements(x).First().Value)

edited Nov 8, 2012 at 19:43

answered Nov 8, 2012 at 19:37

Thom Smith

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1 Comment

Servy Over a year ago

The OP's code is creating an IEnumerable<Dictionary<string,string>>, your's is creating a single dictionary.

Tar · Accepted Answer · 2012-11-08 19:44:33Z

2

The pseudocode is actually pretty close to what you really can do. I assume there's a separate fieldNames collection that you have ready there.

IEnumerable<string> fieldNames = ...;
XDocument doc = ...;
var report1 = doc.Root.Elements("Report1").Elements("Row")
    .Select(report =>
    {
        var d = new Dictionary<string, string>();
        foreach (var fieldName in fieldNames)
        {
            d.Add(fieldName, report.Elements(fieldName).First().Value);
        }
        return d;
    });

answered Nov 8, 2012 at 19:44

Tar

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1 Comment

programmer Over a year ago

+1 because this answer also worked, it's just that Thom Smith was just a min faster at posting his answer.

L.B · Accepted Answer · 2012-11-08 19:57:32Z

1

This will give you a list of type List<Dictionary<string,string>>

var rows = doc.Descendants("Row")
           .Select(r => r.Elements()
                         .ToDictionary(x => x.Name.LocalName, x => x.Value))
           .ToList();

..

var data = rows[i]["Field1"];

edited Nov 8, 2012 at 19:57

answered Nov 8, 2012 at 19:50

L.B

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Comments

Servy · Accepted Answer · 2012-11-08 20:01:48Z

1

Don't try to do everything in a single collection initializer.

For something like this I'd create a separate method:

public static Dictionary<string, string> MapReport(XElement report)
{
    var output = new Dictionary<string, string>();
    foreach(var field in report.Elements())
    {
        output.Add(field.Name, ...);
    }
}

Then the query would be something much simpler:

var report1 = from report in doc.Root.Elements("Report1").Elements("Row")
              select MapReport(report)

edited Nov 8, 2012 at 20:01

answered Nov 8, 2012 at 19:39

Servy

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