C# LINQ query on anonymous types containing dynamic list

Question

I have a piece of C# code where I have created an anonymous type object as follows:

    var measurementUnits = new List<dynamic>() {
    new { Unit = "SQF", Display = new List<string>() { "F", "FT", "SQ FT" }, Ratio=1.5 } ,
    new { Unit = "Hectares", Display = new List<string>() { "H", "HEC"} , Ratio=2.5},
    new { Unit = "Acres", Display = new List<string>() { "AC(TO)" } , Ratio=3.5},
    new { Unit = "SQM", Display = new List<string>() {  "M", "SQ M"}, Ratio=4.5 }
};

Through LINQ I want to access the Ratio where Display="HEC" (case-insensitive) something like:

var multiplier = measurementUnits.Where(m => m.Display == "HEC").First().Ratio;

Is there any reason you're using dynamic here at all? I don't see anything dynamic in what you're doing... why not just create a list of the anonymous type, and keep all the benefits of static typing? — Jon Skeet
– Jon Skeet, Commented Feb 1, 2019 at 9:57
Btw, "H" or "HEC" . You code and description doesn't quite match — Anu Viswan
– Anu Viswan, Commented Feb 1, 2019 at 10:04

Aleks Andreev · Accepted Answer · 2019-02-01 12:07:56Z

4

One possible solution is to avoid dynamic keyword. Try this code

var measurementUnits = new [] {
    new { Unit = "SQF", Display = new List<string>() { "F", "FT", "SQ FT" }, Ratio=1.5 } ,
    new { Unit = "Hectares", Display = new List<string>() { "H", "HEC"} , Ratio=2.5},
    new { Unit = "Acres", Display = new List<string>() { "AC(TO)" } , Ratio=3.5},
    new { Unit = "SQM", Display = new List<string>() {  "M", "SQ M"}, Ratio=4.5 }
};

var multiplier = measurementUnits.Where(m => m.Display.Contains("HEC")).First().Ratio;

Also it would be better to replace First with FirstOrDeafult and manually test it for null, to avoid NullReference exception

var unit = measurementUnits.FirstOrDefault(m => m.Display.Contains("HEC"));
if (unit != null)
    var multiplier = unit.Ratio();

edited Feb 1, 2019 at 12:07

answered Feb 1, 2019 at 10:02

Aleks Andreev

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7 Comments

Tim Schmelter Over a year ago

Only answer that avoids an exception if no such display is contained and also handles that case properly. But you could replace Where with FirstOrDefault(..) to make it even more concise.

Aleks Andreev Over a year ago

@Rango thank you. I believe that we already have enough duplicates of "What is NullReference?" :)

Sujoy Over a year ago

What if I need a case-insensitive search like Contains("HeC") ?

Tim Schmelter Over a year ago

@Sujoy: pass StringComparer.CurrentCultureIgnoreCase, then you aren't using List.Contains anymore but LINQ's extension method Enumerable.Contains

Sujoy Over a year ago

@Rango you are wrong, I get error No overload for method 'Contains' takes '2' arguments'

|

David · Accepted Answer · 2019-02-01 10:08:52Z

Contains would be your best option, yet static typing would be better and not using dynamic.

What is the difference between statically typed and dynamically typed languages?

var measurementUnits = new List<dynamic>() {
     new { Unit = "SQF", Display = new List<string>() { "F", "FT", "SQ FT" }, Ratio=1.5  ,
     new { Unit = "Hectares", Display = new List<string>() { "H", "HEC"} , Ratio=2.5 },
     new { Unit = "Acres", Display = new List<string>() { "AC(TO)" } , Ratio=3.5},
     new { Unit = "SQM", Display = new List<string>() { "M", "SQ M"}, Ratio=4.5 } 
};

var multiplier = measurementUnits.Where(m => m.Display.Contains("HEC")).First().Ratio;

Also you will need to check multiplier for null as your using First this will throw a null reference exception if no value is found, better solution:

var multiplier = measurementUnits.Where(m => m.Display.Contains("HEC")).FirstOrDefault()?.Ratio;

Dmitrii Bychenko · Accepted Answer · 2019-02-01 10:18:35Z

1

Technically you can put something like this (please, note, that Display is a collection which can Contain but not be equal to a single item "H"):

  // 2.5
  var multiplier = measurementUnits
    .First(item => item.Display.Contains("H"))
    .Ratio;

However, I recommend to use a custom class for this, not dynamic which is prone for runtime errors (what if Display is a string, not List<string>).

Edit: If there's a possibility that there's no such an item (say, "HEC2") and you don't want exception be thrown but a default value, change First to FirstOrDefault:

  // 0.0 - default ratio, since "HEC2" is not found
  var multiplier = measurementUnits
    .FirstOrDefault(item => item.Display.Contains("HEC2"))   
   ?.Ratio ?? 0 /* Default Ratio Value Here */;

edited Feb 1, 2019 at 10:18

answered Feb 1, 2019 at 10:01

Dmitrii Bychenko

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3 Comments

Tim Schmelter Over a year ago

You get an exception if there is no such display contained

Dmitrii Bychenko Over a year ago

@Rango: yes, and I think it's a desired behavior (since First() is in the OP's original code)

Tim Schmelter Over a year ago

There is also Where(m=>m.Display=="HEC"), so this is just pseudo code. I wouldn't draw any conclusions from there. As Aleks has said in another comment: " I believe that we already have enough duplicates of What is a NullReferenceException, and how do I fix it?"

Anu Viswan · Accepted Answer · 2019-02-01 10:02:07Z

0

I believe you want to list where Display "has" "HEC", since it is a list. PS: It is unclear in your OP whether you want to filter by "H" or "HEC" (code and description dont match). Assuming it to be "HEC"

var result = measurementUnits.Where(x=>x.Display.Contains("HEC")).Select(x=>x.Ratio);

or If you want the first one

var result = measurementUnits.Where(x=>x.Display.Contains("HEC")).First().Ratio;

answered Feb 1, 2019 at 10:02

Anu Viswan

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Comments

Marco Salerno · Accepted Answer · 2019-02-01 10:08:05Z

0

This is the solution:

var measurementUnits = new [] {
    new { Unit = "SQF", Display = new List<string>() { "F", "FT", "SQ FT" }, Ratio=1.5 } ,
    new { Unit = "Hectares", Display = new List<string>() { "H", "HEC"} , Ratio=2.5},
    new { Unit = "Acres", Display = new List<string>() { "AC(TO)" } , Ratio=3.5},
    new { Unit = "SQM", Display = new List<string>() {  "M", "SQ M"}, Ratio=4.5 }
};
var multiplier = measurementUnits.Where(m => m.Display.IndexOf("H") > -1).FirstOrDefault()?.Ratio;

answered Feb 1, 2019 at 10:08

Marco Salerno

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Comments

Calin Vlasin · Accepted Answer · 2019-02-01 10:27:25Z

0

You cand do this all with FirstOrDefault:

 var multiplier = measurementUnits.FirstOrDefault(x => x.Display.Contains("H"))?.Ratio

answered Feb 1, 2019 at 10:27

Calin Vlasin

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