How to sort property from multiple objects

Question

I have some objects. And in each object there is a propety age. And I want to sort the property age of all the objects. And in this case I have two objects. But for example if you have three, four..etc objects. Maybe there is a more generic method for this?

So this is the code:

List<Person> personList = new List<Person>
{

    new Person { Age = 77 },
    new Person { Age = 88 },
    new Person { Age = 1001 },
    new Person { Age = 755 }
};

List<Dog> dogList = new List<Dog>
{

    new Dog { Age = 1 },
    new Dog { Age = 9 },
    new Dog { Age = 10 },
    new Dog { Age = 8 }
};

personList.Sort((x, y) => x.Age.CompareTo(y.Age));
dogList.Sort((x, y) => x.Age.CompareTo(y.Age));

So the output has to be in this case:

1 8 9 10 77 88 755 1001

You can use quicksort or simply comparison based on ur required value and swap items. Just search for geeksforgeeks quicksort or google — user786
– user786, Commented Oct 7, 2021 at 11:55
Do you just want to sort each list individually? Or get a single sorted list of all Age values from each list? — devNull
– devNull, Commented Oct 7, 2021 at 11:57

StuartLC · Accepted Answer · 2021-10-08 09:33:59Z

3

In addition to Christian's approach of mutating / extending an existing list with Concat, it's also possible to do this without materializing the projections and using Union to produce a new combined sequence, before ordering, like so:

var sortedAges = personList
    .Select(p => p.Age)
    .Union(dogList.Select(d => d.Age))
    .OrderBy(age => age);

foreach (var age in sortedAges) // << The result is only 'materialized' here, once.
{ ...

edited Oct 8, 2021 at 9:33

answered Oct 7, 2021 at 12:09

StuartLC

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2 Comments

Jeremy Thompson Over a year ago

it's also possible to do this without materializing the projections - can you please give other readers (including me) a link to read up on this. Without adding a new question I'm interested in the way algorithms and data types are chosen depending on the LINQ. Thanks

StuartLC Over a year ago

Good point. I can't find an absolutely 'definitive' guide to lazy evaluation / aka deferred execution (suggest google around), but essentially IEnumerable and IQueryable enable 'stream' type processing, as opposed to concrete in memory processing (like a List, Array etc). There are pros and cons of either approach, but its always good to really know what's going on under the hood, especially when dealing with large data sources and also IQueryable sources like Entity Framework / ORMs, where materialization will actually execute a query on the database.

Christian Phillips · Accepted Answer · 2021-10-07 12:01:45Z

2

You could create two lists of the ages which will create an IEnumerable<int>, and Combine and Order them...

var personAsAge = personList.Select(p => p.Age);
var dogAsAge = Dogist.Select(d => d.Age);

var ageOrder = personAsAge.Concat(dogAsAge).OrderBy(a => a);

You will need to import System.Linq; too.

edited Oct 7, 2021 at 12:01

answered Oct 7, 2021 at 11:53

Christian Phillips

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