I have the following scenario:
I get a collection of records from a data source and add them to a List
List<Entity> e = new List<Entity>();
foreach (var elm in datasource)
{
e.Add(new Entity { First = elm.First, Second = elm.Second, Third = elm.Third });
}
This gives me something like:
// -> First = John, Second = Sally, Third = Ingrid
// -> First = Sally, Second = Ingrid, Third = James
// -> First = Ingrid, Second = Sally, Third = James
I have an array of possible values that can be true and possible values that can be negative, in a List
List<string> positives = { "John", "Sally" }
List<string> negatives = { "Ingrid", "James" }
I am looking for an elegant why of matching the amount of positives and the amount of negatives I have in the generic list e, as per the above? Would something like this be possible with LINQ?
As I am not familiar with LINQ have no idea where to start. I tried something like:
var pos = e.SelectMany(s => s in positives).Count()
But this throws an exception.
Any help would be greatly appreciated
SQL's in clause in LINQ is Contains method.
Test:
var pos = e.SelectMany(s => positives.Contains(s)).Count();
Seems that I haven't understood your question. Reading again.
To be honest, your question in not well-phrased.
But based on what I understood, I think the correct response is:
var pos = e.SelectMany(i => positives.Contains(i.First)
|| positives.Contains(i.Second)
|| positives.Contains(i.Third)).Count();
You are using in incorrectly
e.SelectMany(s => positives.Contains(s)).Count();
but what I assue you are wanting is this
var pos = e.Count(s => positives.Contains(s.First) || positives.Contains(s.Second) ||positives.Contains(s.Third));
var neg= e.Count(s => negatives.Contains(s.First) || negatives.Contains(s.Second) ||negatives.Contains(s.Third));
or you can use an any
var pos = e.SelectMany(i =>
positives.Any(p=> p==i.First || p==i.Second || p==i.Third))
.Count();
Related
I need to iterate through all items in a subtree.
Therefore, I want to put all childItems of an predecessor into an array. I tried:
var successors =
TabWebContext.MenuItemSet.Where(m => m.PredecessorId == parentId).ToArray();
I also tried it without .ToArray() and with .ToList().
I have the following loop: while (successors.Count()>0){...} (or rather .Length>0).
The condition is never true.
What do you think am I making wrong? I know there are elements (if I do .FirstOrDefault(), there is at least one element found.
Why do you feel that it needs to be in an array to iterate through it? You could iterate the list like this:
foreach (var successor in TabWebContext.MenuItemSet.Where(m => m.PredecessorId == parentId))
{
// do stuff with 'successor'
}
Just to show an example of how select all from data source works with where clause.
int[] numbers = { 2, 34, 23, 11 }; //data source >> can be EF or ADO.NET
var result = numbers.Where(n => n <= 20).ToList(); // select all with filteration
foreach(int i in result ) //just to loop and
{
Console.WriteLine(i);
}
output :
22
11
so there is no issue can be seen in var successors =
TabWebContext.MenuItemSet.Where(m => m.PredecessorId == parentId).ToArray();
if you do facing an error then show that in your question.
I'm facing this exception when I'm using String.Split with random strings.
List<string> linhas = new List<string>();
linhas.Add("123;abc");
linhas.Add("456;def");
linhas.Add("789;ghi");
linhas.Add("chocolate");
var novas = linhas.Where(l => l.ToString().Split(';')[1]=="def");
The last string "chocolate"doesn't contain a ";", so String.Split returns an array with a single string "chocolate". That's why you get the exception if you try to accesss the second.
You could use ElementAtOrDefault which returns null for strings instead:
var novas = linhas.Where(l => l.Split(';').ElementAtOrDefault(1) == "def");
A longer approach using an anonymous type:
var novas = linhas
.Select(l => new { Line = l, Split = l.Split(';') })
.Where(x => x.Split.Length >= 2 && x.Split[1] == "def")
.Select(x => x.Line);
I'm going to expand a little on Tim's answer and show a way to do a few extra things within your LINQ queries.
You can expand the logic within you Where clause to do some additional processes, which can make your code a bit more readable. This would be good for something small:
var novas = linhas.Where(l =>
{
var parts = l.Split(':');
return parts.Length > 1 ? parts[1] == "def" : false;
});
If you need multiple statements, you can wrap the body of your clause within curly braces, but then you need the return keyword.
Alternatively, if you have a lot of information that would make something inline like that unreadable, you can also use a separate method within your query.
public void FindTheStringImLookingFor()
{
var linhas = new List<string>();
linhas.Add("123;abc");
linhas.Add("456;def");
linhas.Add("789;ghi");
linhas.Add("chocolate");
var words = linhas.Where(GetTheStringIWant);
}
private bool GetTheStringIWant(string s)
{
var parts = s.Split(':');
// Do a lot of other operations that take a few lines.
return parts.Length > 1 ? parts[1] == "def" : false;
}
If I want to find the exact match or the next nearest for a string.
Using SQL, I can do :
SELECT TOP 1 *
FROM table
WHERE Code >= #searchcode
ORDER BY Code
How might I achieve this using LINQ and a List of the records.
I was expecting to be able to do something like:
var find = ListDS.Where(c => c.Code >= searchcode).First();
but you can't compare strings that way.
Note that Code is an alpha string, letters, numbers, symbols, whatever..
Nearest means if you have a list containing "England", "France", "Spain", and you search for "France" then you get "France". If you search for "Germany" you get "Spain".
Here is a simple code may help you
List<string> ls = new List<string>();
ls.Add("ddd");
ls.Add("adb");
var vv = from p in ls where p.StartsWith("a") select p;
select all element with starting string "a"
If Code is an int this might work:
var find = ListDS.Where(c => c.Code >= searchcode).OrderBy(c => c.Code).First();
otherwise you need to convert it to one:
int code = int.Parse(searchcode);
var find = ListDS.Where(c => Convert.ToInt32(c.Code) >= code).OrderBy(c => Convert.ToInt32(c.Code)).First();
Try this solution:
class Something
{
public string Code;
public Something(string code)
{
this.Code = code;
}
}
class Program
{
static void Main(string[] args)
{
List<Something> ListDS = new List<Something>();
ListDS.Add(new Something("test1"));
ListDS.Add(new Something("searchword1"));
ListDS.Add(new Something("test2"));
ListDS.Add(new Something("searchword2"));
string searchcode = "searchword";
var find = ListDS.First(x => x.Code.Contains(searchcode));
Console.WriteLine(find.Code);
Console.ReadKey();
}
}
I replaced your >= with .Contains. You can also add the action into First, no need for Where.
It will not find the "nearest", just the first word containg your search parameters.
You could compare string in C#, it will use alphabetically order:
var find = ListDS.Where(c => c.Code.CompareTo(searchcode) >= 0)
.OrderBy(c => c) // get closer one, need to order
.First();
See the CompareTo docs.
Note that with this method, "10" > "2".
I'm constructing a linq query that will check is a string in the DB contains any of the strings in a list of strings.
Something like.
query = query.Where(x => x.tags
.Contains(--any of the items in my list of strings--));
I'd also like to know how many of the items in the list were matched.
Any help would be appreciated.
Update: I should have mentioned that tags is a string not a list. And I am adding on a couple more wheres that are not related to tags before the query actually runs. This is running against entity framework.
EDIT: This answer assumed that tags was a collection of strings...
It sounds like you might want:
var list = new List<string> { ... };
var query = query.Where(x => x.tags.Any(tag => list.Contains(tag));
Or:
var list = new List<string> { ... };
var query = query.Where(x => x.tags.Intersect(list).Any());
(If this is using LINQ to SQL or EF, you may find one works but the other doesn't. In just LINQ to Objects, both should work.)
To get the count, you'd need something like:
var result = query.Select(x => new { x, count = x.tags.Count(tag => list.Contains(tag)) })
.Where(pair => pair.count != 0);
Then each element of result is a pair of x (the item) and count (the number of matching tags).
I've done something like this before:
var myList = new List<string>();
myList.Add("One");
myList.Add("Two");
var matches = query.Where(x => myList.Any(y => x.tags.Contains(y)));
like this:
List<string> list = new List<string>();
list.Add("One");
list.Add("Two");
var result = query.Where(x => list.Contains(x.tags));
I am not quite sure from your question if x.tags is a string or list, if it is a list Jon Skeet's answer is correct. If I understand you correctly though x.tags is a string of strings. If so then the solution is:
list.Any(x => x.tags.IndexOf(x) > -1)
to count them do
list.Count(x => x.tags.IndexOf(x) > -1)
var t = new List<string> { "a", "b", "c" };
var y = "a b d";
var res = y.Count(x => t.Contains(x.ToString()));
I faced a similar problem recently and here's how I managed to work it out:
var list = [list of strings];
if (list != null && list.Any())
{
queryable = queryable.Where(x => x.tags != null);
var tagQueries = new List<IQueryable<WhateverTheDbModelIs>>();
foreach (var element in list)
{
tagQueries.Add(queryable.Where(x => x.tags.Contains(element)));
}
IQueryable<WhateverTheDbModelIs> query = tagQueries.FirstOrDefault();
foreach (var tagQuery in tagQueries)
{
query = query.Union(tagQuery);
}
queryable = queryable.Intersect(query);
}
probably not the best option but something a less experienced developer can understand and use
Here is some sample code I have basically written thousands of times in my life:
// find bestest thingy
Thing bestThing;
float bestGoodness = FLOAT_MIN;
foreach( Thing x in arrayOfThings )
{
float goodness = somefunction( x.property, localvariable );
if( goodness > bestGoodness )
{
bestGoodness = goodness;
bestThing = x;
}
}
return bestThing;
And it seems to me C# should already have something that does this in just a line. Something like:
return arrayOfThings.Max( delegate(x)
{ return somefunction( x.property, localvariable ); });
But that doesn't return the thing (or an index to the thing, which would be fine), that returns the goodness-of-fit value.
So maybe something like:
var sortedByGoodness = from x in arrayOfThings
orderby somefunction( x.property, localvariable ) ascending
select x;
return x.first;
But that's doing a whole sort of the entire array and could be too slow.
Does this exist?
This is what you can do using System.Linq:
var value = arrayOfThings
.OrderByDescending(x => somefunction(x.property, localvariable))
.First();
If the array can be empty, use .FirstOrDefault(); to avoid exceptions.
You really don't know how this is implemented internally, so you can't assure this will sort the whole array to get the first element. For example, if it was linq to sql, the server would receive a query including the sort and the condition. It wouldn't get the array, then sort it, then get the first element.
In fact, until you don't call First, the first part of the query isn't evaluated. I mean this isn't a two steps evaluation, but a one step evaluation.
var sortedValues =arrayOfThings
.OrderByDescending(x => somefunction(x.property, localvariable));
// values isn't still evaluated
var value = sortedvalues.First();
// the whole expression is evaluated at this point.
I don't think this is possible in standard LINQ without sorting the enuermable (which is slow in the general case), but you can use the MaxBy() method from the MoreLinq library to achieve this. I always include this library in my projects as it is so useful.
http://code.google.com/p/morelinq/source/browse/trunk/MoreLinq/MaxBy.cs
(The code actually looks very similar to what you have, but generalized.)
I would implement IComparable<Thing> and just use arrayOfThings.Max().
Example here:
http://msdn.microsoft.com/en-us/library/bb347632.aspx
I think this is the cleanest approach and IComparable may be of use in other places.
UPDATE
There is also an overloaded Max method that takes a projection function, so you can provide different logic for obtaining height, age, etc.
http://msdn.microsoft.com/en-us/library/bb534962.aspx
I followed the link Porges listed in the comment, How to use LINQ to select object with minimum or maximum property value and ran the following code in LINQPad and verified that both LINQ expressions returned the correct answers.
void Main()
{
var things = new Thing [] {
new Thing { Value = 100 },
new Thing { Value = 22 },
new Thing { Value = 10 },
new Thing { Value = 303 },
new Thing { Value = 223}
};
var query1 = (from t in things
orderby GetGoodness(t) descending
select t).First();
var query2 = things.Aggregate((curMax, x) =>
(curMax == null || (GetGoodness(x) > GetGoodness(curMax)) ? x : curMax));
}
int GetGoodness(Thing thing)
{
return thing.Value * 2;
}
public class Thing
{
public int Value {get; set;}
}
Result from LinqPad