I have a dictionary with following Structure
Dictionary<string, List<string>>
I want to extract all the values of the above dictionary and pass as list of strings to another method.
like
MyMethod(List<string>)
Do we have an efficient way to do this without foreach loop?
Assuming you mean you want all values as a flat list, you can use LINQ:
var myDict = new Dictionary<string, List<string>>();
var allValues = myDict.Values.SelectMany(v => v).ToList();
.SelectMany will flatten the enumerable returned from the expression v => v.
If you're using .NET Core in Visual Studio, you might need to add using System.Linq; to the top of the file.
Related
So basically I'm having an issue with the task I've been given. I won't bore you with the details of the task itself so I'll just give you the relevant info.
I have a dictionary that I need to be sorted by the int[value] that is the highest, well the top five highest to be precise and I need to be able to show the bottom five as well.
Dictionary<string, int> dict = new Dictionary<string, int>();
The strings(keys) hold words that have been read for a text file. The ints (values) hold ints of how many times they were mentioned in the document.
I was going to do it in another way but I was told to do it with a dictionary so please dictionary only help.
I would appreciate it if you can explain how it should be done so I can learn as well as complete the task as the aim of the task is to educate myself but I'm finding it a bit hard..
I appreciate all your help in advance, if more info is required please let me know and I'll post it!
Dictionaries do not have any inherent order. But if you want to get the top 5 entries with highest (or lowest) values, you can use a little Linq:
using System.Linq;
...
var top5 = dict.OrderByDescending(pair => pair.Value).Take(5);
var bottom5 = dict.OrderBy(pair => pair.Value).Take(5);
This will return an IEnumerable<KeyValuePair<string, int>>. To turn it back into a dictionary, again Linq can help. For example:
var top5 = dict.OrderByDescending(pair => pair.Value).Take(5)
.ToDictionary(pair => pair.Key, pair => pair.Value);
Now, top5 is a Dictionary<string, int> which contains only the 5 elements from dict with the hightest value.
You need to get ordered result from your dictionary, Since you are looking for Top 5, you will need Take like:
//Top 5
foreach (var item in dict.OrderByDescending(r => r.Value).Take(5))
{
Console.WriteLine("Key: {0}, Value: {1}", item.Key, item.Value);
}
The reason you need an OrderBy is because:
Dictionary<TKey, TValue> Class
For purposes of enumeration, each item in the dictionary is treated as
a KeyValuePair structure representing a value and its
key. The order in which the items are returned is undefined.
If you are using C# 3.0 and higher
You can do something like this with LINQ
foreach (KeyValuePair<string,int> item in keywordCounts.OrderBy(key=> key.Value).Take(5))
{
// do something with item.Key and item.Value
}
If you are using C# 2.0
List<KeyValuePair<string, string>> myList = aDictionary.ToList();
myList.Sort((firstPair,nextPair) =>
{
return firstPair.Value.CompareTo(nextPair.Value);
}
);
or it can be rewritten as
myList.Sort((x,y)=>x.Value.CompareTo(y.Value));
LINQ allows for great flexibility in that you can select the top 10, 20 10% etc. Or if you are using your word frequency index for type-ahead, you could also include StartsWith clause as well.
In windows phone, I retrieved a table in database as dictionary in LINQ. My dictionary is like this
Dictionary<int, StudentTable>
I retrieved the table from LINQ as
var studentDictionary = studContext.StudentList.Select(p => new { p.RollNo, p }).AsEnumerable().ToDictionary(kvp => kvp.RollNo, kvp => kvp);
But I want to get all the values in the studentDictionary as a
List<StudentTable>
I know it is possible by adding each dictionary values to the list by using for loop.
How can I do this without a loop. ?
Is there any other better method than a loop?
Thanks
You can use studentDictionary.Values.
PS: The same works for the keys, using studentDictionary.Keys
Your dictionary contains Value which is an object of type StudentTable. You can select that from the dictionary and apply ToList method.
var list = studentDictionary.Values.ToList();
or
var list = studentDictionary.Select(r => r.Value).ToList();
I have the following declaration:
Dictionary<string, Dictionary<string, string>> like = new Dictionary<string, Dictionary<string, string>>();
I need to get the first element out, but do not know the key or value. What's the best way to do this?
Note that to call First here is actually to call a Linq extension of IEnumerable, which is implemented by Dictionary<TKey,TValue>. But for a Dictionary, "first" doesn't have a defined meaning. According to this answer, the last item added ends up being the "First" (in other words, it behaves like a Stack), but that is implementation specific, it's not the guaranteed behavior. In other words, to assume you're going to get any defined item by calling First would be to beg for trouble -- using it should be treated as akin to getting a random item from the Dictionary, as noted by Bobson below. However, sometimes this is useful, as you just need any item from the Dictionary.
Just use the Linq First():
var first = like.First();
string key = first.Key;
Dictionary<string,string> val = first.Value;
Note that using First on a dictionary gives you a KeyValuePair, in this case KeyValuePair<string, Dictionary<string,string>>.
Note also that you could derive a specific meaning from the use of First by combining it with the Linq OrderBy:
var first = like.OrderBy(kvp => kvp.Key).First();
For anyone coming to this that wants a linq-less way to get an element from a dictionary
var d = new Dictionary<string, string>();
d.Add("a", "b");
var e = d.GetEnumerator();
e.MoveNext();
var anElement = e.Current;
// anElement/e.Current is a KeyValuePair<string,string>
// where Key = "a", Value = "b"
I'm not sure if this is implementation specific, but if your Dictionary doesn't have any elements, Current will contain a KeyValuePair<string, string> where both the key and value are null.
(I looked at the logic behind linq's First method to come up with this, and tested it via LinqPad 4)
Though you can use First(), Dictionaries do not have order per se. Please use OrderedDictionary instead. And then you can do FirstOrDefault. This way it will be meaningful.
EDIT:
Use an OrderedDictionary.
It's better to use FirstOrDefault() to retrieve the first value.
Ex:
var firstElement = like.FirstOrDefault();
string firstElementKey = firstElement.Key;
Dictinary<string,string> firstElementValue = firstElement.Value;
Dictionary does not define order of items. If you just need an item use Keys or Values properties of dictionary to pick one.
using System.Linq;
Dictionary<string, Dictionary<string, string>> like = new Dictionary<string, Dictionary<string, string>>();
Dictionary<string, string> first = like.Values.First();
ill find easy way to find first element in Dictionary :)
Dictionary<string, Dictionary<string, string>> like =
newDictionary<string,Dictionary<string, string>>();
foreach(KeyValuePair<string, Dictionary<string, string>> _element in like)
{
Console.WriteLine(_element.Key); // or do something
break;
}
convert to Array
var array = like.ToArray();
var first = array[0];
Easy way of to index a Collection in terms of performance, high compatibility (2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8) and easy implemention.
Save today!!
Its not only a items copy, this is items reference of a Collection!!
buy it!!
string [] arrayString = new string[like.Count];
like.Values.CopyTo( arrayString,0 );
arrayString[0] //First
References:
https://learn.microsoft.com/es-es/dotnet/api/system.collections.generic.icollection-1.copyto?view=net-5.0
https://social.msdn.microsoft.com/Forums/vstudio/en-US/dc5e4242-64d3-45ac-bdea-cf4f3d9abdbb/icollectioncopyto-vs-arraylisttoarray?forum=netfxbcl
I have one Dictionary and added some elements on it.for example,
Dictionary<string, string> d = new Dictionary<string, string>();
d.Add("Content","Level0");
d.Add("gdlh","Level1");
d.Add("shows","Level2");
d.Add("ytye","Level0");
In C#, Dictionary keeps elements in natural order.But i now want to iterate those values from last to first(ie, Reverse order).i mean,
first i want to read ytye then shows,gdlh and finally Content.
Please guide me to get out of this issue...
Just use the Linq extension method Reverse
e.g.
foreach( var item in d.Reverse())
{
...
}
Use LINQ Reverse, but note that does not reverse in place:
var reversed = d.Reverse();
But note that this is not a SortedDictionary, so the order is not necessarily guaranteed in the first place. Perhaps you want OrderByDescending instead?
Maybe OrderByDescending on the key. Like this:
d.OrderByDescending (x =>x.Key)
Foreach like this:
foreach (var element in d.OrderByDescending (x =>x.Key))
{
}
It's available with Linq: d.Reverse()
I'm trying to locate all the keys in one Dictionary that are not in another Dictionary. Obviously, I can do this using a nested loop, but I'm trying to learn LINQ at the moment and I was wondering if I might use it to accomplish this task?
Here's what I have so far:
Dictionary<string, List<string>> DBtables = this.CollectTableListings();
var generic = from Dictionary<string,List<string>> tab
in DBtables
where !_tables.ContainsKey(???)
select tab;
Any idea what should go in place of the question marks (or perhaps instead of the entire where clause)?
You can do:
var resultKeys = DBTables.Keys.Except( _tables.Keys );
The Except() method is essentially the same as the minus operations in SQL - it returns all items from the first collection excluding those in the second. Since dictionaries expose their keys, you can compute their difference that way.
The Except() operator uses the default equality for the type, but there is also an overload which allows you to specify your own IEqualityComparer to override the semantics of how to compare values. In your example, you probably don't need that - but it's nice to know it there.
Dictionary<string, List<string>> dictOne = ...
Dictionary<string, List<string>> dictTwo = ...
var missingKeys = dictOne.Keys.Where(x => !dictTwo.ContainsKey(x));
Dictionary<string, List<string>> dictionary = this.CollectTableListings();
Dictionary<string, List<string>> otherDictionary = getOtherTable();
var keys = from key in dictionary.Keys
where !otherDictionary.Keys.Contains(key)
select key;
(But LBuskin's answer is much better)
have a look at the Except extension method. HTH.
If you wanted to use query syntax I would do something akin to below:
var keys = from d1 in dictionary1
select d1.Key;
var items = from d2 in dictionary2
where d2.Key in keys
select d2;
foreach(var item in items)
{
}