I have a linq query that returns a list of MyObject. I'd like to add a property to MyObject called TheIndex and that contains the ordinate of the item in the sequence.
In other words, I need something like this:
var TheResult = from d in MyDataContext
where.....
select new MyObject
{
Property1 = d.whatever,
TheIndex = ?
}
The query returns a list of MyObject and I'd like each item in the list to contain the index as one of its property.
Thanks.
Once you get away from the query syntax, you'll find a Select overload that gives you the index you're looking for.
var result = MyDataContext
.Where(d => d.Prop == "A")
.AsEnumerable()
.Select((d, i) =>
new MyObject() {
Property1 = d.whatever,
TheIndex = i
});
Related
The basic question
I have:
IEnumerable<string> listA
var listB (this is an anonymous list generated by a LINQ query)
I want to query a list of objects that contain listA to see if they match to listB:
someObjectList.Where(x => x.listA == listB)
The comparison doesn't work - so how do I ensure that both lists are the same type for comparison?
The detailed question
I am grouping a larger list into a subset that contains a name and related date(s).
var listGroup = from n in list group n by new
{ n.NAME } into d
select new
{
NAME = d.Key.NAME, listOfDates = from x in d select new
{ Date = x.DATE } };
I have a object to hold the values for further processing:
class SomeObject
{
public SomeObject()
{
_listOfDates = new List<DateTime>();
}
private IEnumerable<DateTime> _listOfDates;
public IEnumerable<DateTime> ListOfDates
{
get { return _listOfDates; }
set { _listOfDates = value; }
}
}
I am then iterating over the listGroup and adding into a generic List<> of SomeObject:
foreach(var item in listGroup)
{
SomeObject so = new SomeObject();
// ...do some stuff
if (some match occurs then add into List<SomeObject>)
}
As I iterate through then I want to check the existing List<SomeOjbect> for matches:
var record = someObjectList.Where(x => x.NAME == item.NAME &&
x.ListOfDates == item.listOfDates)
.SingleOrDefault();
The problem is that comparing x.ListOfDates against item.listOfDates doesn't work.
There is no compiler error but I suspect that the returned value lists are different. How to I get the lists to commonize so they can be compared?
Update #1
This seems to work to get the listOfDates into a similar format:
IEnumerable<DateTime> tempList = item.listOfDates.Select(x => x.DATE).ToList()
Then I followed the 'SequenceEqual' suggestion from #Matt Burland
You can just compare one IEnumerable<DateTime> to another IEnumerable<DateTime>, you need to compare the sequence. Luckily, there's Enumerable.SequenceEquals (in both static and extension method flavors) which should work here.
So something like:
var record = someObjectList
.Where(x => x.NAME == item.NAME && x.ListOfDates.SequenceEquals(item.listOfDates))
.SingleOrDefault();
I have a linq query that works when it I had a list of a single value now that I change to having a List that has several properties I need to change the where clause
So this works:
List<string> etchList = new List<string>();
etchList.Add("24");
var etchVect = (from vio in AddPlas
where etchList.Any(v => vio.Key.Formatted.Equals(v))
let firstOrDefault = vio.Shapes.FirstOrDefault()
where firstOrDefault != null
select new
{
EtchVectors = firstOrDefault.Formatted
}).ToList();
However I have a new hard coded list (which will represent incoming data:
List<ExcelViolations> excelViolations = new List<ExcelViolations>();
excelViolations.Add(new ExcelViolations
{
VioID = 24,
RuleType = "SPACING",
VioType = "Line-Line",
XCoordinate = 6132,
YCoordinate = 10031.46
});
So the NEW Linq query looks like this, but is obviously will not work as
AddPlas is a List and so using this other list of excelviolations, I wish to have it do where on each one of the properties in the excelviolations list
var etchVect = (from vio in AddPlas
where excelViolations.Any(vioId => vio.Key.Formatted.Equals(vioId))
let firstOrDefault = vio.Shapes.FirstOrDefault()
select new
{
EtchVectors = firstOrDefault.Formatted
}).ToList();
Now, since this is a list within a list, I would like to do something like add in each of the properties
so for example:
where excelViolations.VioID.Any(vioId => vio.Key.Formatted.Equals(vioId))
However that is not possible, but you see that I'm trying to access the property of VioID that is in the excelViolations and match it to the Key which is in vio list
Just change this line
where excelViolations.Any(vioId => vio.Key.Formatted.Equals(vioId))
to
where excelViolations.Any(excelVio => vio.Key.Formatted.Equals(excelVio.VioID))
then i thought it will works
I have below code in c# 4.0.
//Dictionary object with Key as string and Value as List of Component type object
Dictionary<String, List<Component>> dic = new Dictionary<String, List<Component>>();
//Here I am trying to do the loping for List<Component>
foreach (List<Component> lstComp in dic.Values.ToList())
{
// Below I am trying to get first component from the lstComp object.
// Can we achieve same thing using LINQ?
// Which one will give more performance as well as good object handling?
Component depCountry = lstComp[0].ComponentValue("Dep");
}
Try:
var firstElement = lstComp.First();
You can also use FirstOrDefault() just in case lstComp does not contain any items.
http://msdn.microsoft.com/en-gb/library/bb340482(v=vs.100).aspx
Edit:
To get the Component Value:
var firstElement = lstComp.First().ComponentValue("Dep");
This would assume there is an element in lstComp. An alternative and safer way would be...
var firstOrDefault = lstComp.FirstOrDefault();
if (firstOrDefault != null)
{
var firstComponentValue = firstOrDefault.ComponentValue("Dep");
}
[0] or .First() will give you the same performance whatever happens.
But your Dictionary could contains IEnumerable<Component> instead of List<Component>, and then you cant use the [] operator. That is where the difference is huge.
So for your example, it doesn't really matters, but for this code, you have no choice to use First():
var dic = new Dictionary<String, IEnumerable<Component>>();
foreach (var components in dic.Values)
{
// you can't use [0] because components is an IEnumerable<Component>
var firstComponent = components.First(); // be aware that it will throw an exception if components is empty.
var depCountry = firstComponent.ComponentValue("Dep");
}
You also can use this:
var firstOrDefault = lstComp.FirstOrDefault();
if(firstOrDefault != null)
{
//doSmth
}
for the linq expression you can use like this :
List<int> list = new List<int>() {1,2,3 };
var result = (from l in list
select l).FirstOrDefault();
for the lambda expression you can use like this
List list = new List() { 1, 2, 3 };
int x = list.FirstOrDefault();
You can do
Component depCountry = lstComp
.Select(x => x.ComponentValue("Dep"))
.FirstOrDefault();
Alternatively if you are wanting this for the entire dictionary of values, you can even tie it back to the key
var newDictionary = dic.Select(x => new
{
Key = x.Key,
Value = x.Value.Select( y =>
{
depCountry = y.ComponentValue("Dep")
}).FirstOrDefault()
}
.Where(x => x.Value != null)
.ToDictionary(x => x.Key, x => x.Value());
This will give you a new dictionary. You can access the values
var myTest = newDictionary[key1].depCountry
Try this to get all the list at first, then your desired element (say the First in your case):
var desiredElementCompoundValueList = new List<YourType>();
dic.Values.ToList().ForEach( elem =>
{
desiredElementCompoundValue.Add(elem.ComponentValue("Dep"));
});
var x = desiredElementCompoundValueList.FirstOrDefault();
To get directly the first element value without a lot of foreach iteration and variable assignment:
var desiredCompoundValue = dic.Values.ToList().Select( elem => elem.CompoundValue("Dep")).FirstOrDefault();
See the difference between the two approaches: in the first one you get the list through a ForEach, then your element. In the second you can get your value in a straight way.
Same result, different computation ;)
There are a bunch of such methods:
.First .FirstOrDefault .Single .SingleOrDefault
Choose which suits you best.
var firstObjectsOfValues = (from d in dic select d.Value[0].ComponentValue("Dep"));
I would to it like this:
//Dictionary object with Key as string and Value as List of Component type object
Dictionary<String, List<Component>> dic = new Dictionary<String, List<Component>>();
//from each element of the dictionary select first component if any
IEnumerable<Component> components = dic.Where(kvp => kvp.Value.Any()).Select(kvp => (kvp.Value.First() as Component).ComponentValue("Dep"));
but only if it is sure that list contains only objects of Component class or children
I want to select elements from myCollection using myFilters for filtering:
var myFilters = new List<string> {"111", "222"};
var myCollection = new List<SomeClass> {
new SomeClass ("111"),
new SomeClass ("999")
};
from filter in myFilters
from item in myCollection
where item.Name == filter
select item
would return the "111" item.
However, if myFilters is empty I want to return all the items from myCollection.
var myFilters = new List<string> ();
var myCollection = new List<SomeClass> {
new SomeClass ("111"),
new SomeClass ("999")
};
// Here's where I'm lost...
from filter in myFilters
from item in myCollection
where item.Name == filter
select item
would return all items ("111" and "999").
If these collections are going to be sizable, then I recommend using a join. It would look something like this:
var result =
myFilters.Any() ?
from item in myCollection
join filter in myFilters
on item.Name equals filter into gj
where gj.Any()
select item
: myCollection;
Opportunities for using joins are easily overlooked. This join approach will outperform the contains approach when the lists are remotely large. If they're small and performance is acceptable, then use whichever seems the clearest.
var result = myCollection
.Where(i => (!myFilters.Any() || myFilters.Contains(i.Name)));
The best you're going to be able to do is project the filters into SomeClass. Something like:
var results = myCollection.Any() ?
myCollection.Where(item => myFilters.Contains(item.Name)) :
myFilters.Select(f => new SomeClass (f));
How about this?
var myFilters = new List<string> ();
var myCollection = new List<SomeClass> {new SomeClass ("111"), new SomeClass ("999")};
// Here's where I'm lost...
from filter in myFilters
from item in myCollection
where item.Name == filter || !myFilters.Any()
select item
Selecting from two collections performs a join based on your where clause. The join condition above says join on item.Name equal to filter OR select it if there are no filters available.
Try this:
var result = myCollection.Where(s => !myFilters.Any() ||
myFilters.Contains(s.Name));
//EDIT: commented these lines..based on comment by #Servy
//var result = myCollection.Where(s => myFilters.Count == 0 ||
// myFilters.Contains(s.Name));
Maybe it would be better to count filter collection only once:
bool isFilterEmpty = !myFilters.Any();
//bool isFilterEmpty = myFilters.Count == 0; //...or like this
var result = myCollection.Where(s => isFilterEmpty ||
myFilters.Contains(s.Name));
EDIT
I'd even say that the answer by #itsme86 is correct, but, I guess, he has confused your collections. So his answer should look somehow like this:
var results = myFilters.Any()
? myCollection.Where(item => myFilters.Contains(item.Name))
: myCollection;
I have a list of class items List<MyClass>
I have a seperate object that is of type MyClass
In my list I have an instance of this item but my where statement fails.
var home = Item.Find(23);
var item = allitems.Where(i => i == home);
item yields no results
allitems.Contains(home) also fails.
What am I doing wrong?
Are they definately tghe same items? If you have this situation;
var item1 = new Place(23);
var item2 = new Place(23);
then item1 != item2. If the items are identified by some property, you could try
allitems.Where(i => i.Id == home.Id)
Overriding Equals() in "Item" should also work.
var home = Item.Find(23);
var item = allitems.Where(i => i.Equals(home));