I have a problem similar to the following post:
How to merge two didctionaries in C# with duplicates
However, in the post, the solution concatenates duplicate strings. I want to do something similar, but with integers, and I don't want to concatenate them, I want to add them.
So I want this:
var firstDic = new Dictionary<string, int>
{
{"apple", 1},
{"orange", 2}
};
var secondDic = new Dictionary<string, int>
{
{"apple", 3},
{"banana", 4}
};
To be unioned in some way to become:
var thirdDic = new Dictionary<string, int>
{
{"apple", 4}, //values from the two "apple" keys added together.
{"orange", 2},
{"banana", 4}
};
Is there any quick and easy way to do this without having to do some cumbersome nested loop mess?
Just use Sum:
var thirdDic = firstDic.Concat(secondDic)
.GroupBy(o => o.Key)
.ToDictionary(o => o.Key, o => o.Sum(v => v.Value));
Related
I'm trying to find the most "elegant" way to deal with the transformation between two collections using LINQ. The source container type is Dictionary<int, List<string>> and I need to convert it to List<KeyValuePair<string, string>>. Basically I need to duplicate the key in the dictionary for every element in its corresponding list into a flattened list. Below shows my 2 attempts to solve the issue.
Dictionary<int, List<string>> source = new() {
{100, new() {"a", "b", "c"}}
};
List<KeyValuePair<string, string>> target = new();
// Solution 1
foreach (var (score, terms) in source)
{
foreach (var term in terms)
{
target.Add(new KeyValuePair<string, string>(score.ToString(), term));
}
}
// Solution 2
target = source.SelectMany(kvp =>
{
var(score, terms) = kvp;
return terms.Select(t => new KeyValuePair<string, string>(score.ToString(), t));
}).ToList();
Runnable sample here on .NET Fiddle.
I'm using .NET Core 5 and C# 9 in a console application.
Both of these work, I think, but I want to see if I can make this cleaner. It's pretty difficult to find out how to use LINQ to solve complex transformations like this. One thing I tried to do was "deconstruct" the KeyValuePair in SelectMany(), like:
source.SelectMany((score, terms) => ...)
But this didn't work. I'm not sure if there's a way to make that kind of deconstruction possible. Little things like this I think could go a long way to making this cleaner.
Maybe
var results = source
.SelectMany(x => x.Value
.Select(y => new KeyValuePair<string, string>(x.Key.ToString(), y)))
.ToList();
Or if you are happy with Value Tuples (which have a few benefits)
var results = source
.SelectMany(x => x.Value
.Select(y => (x.Key.ToString(), y)))
.ToList();
If you want to pattern match it in a single expression ("that kind of deconstruction"), you can abuse (?) the switch expression:
target = source.SelectMany(kvp => kvp switch { var (score, terms) =>
terms.Select(t => new KeyValuePair<string, string>(score.ToString(), t))
}).ToList();
You can use the overload of SelectMany that has a parameter resultSelector.
var results = source.SelectMany(sourceItem => sourceItem.Value,
// parameter resultSelector:
(sourceItem, listItem) => ...
In baby steps:
Source is a sequence of KeyValuePair<int, List<string>>. So every sourceItem is one KeyValuePair<int, List<string>>. sourceItem.Value is the List<string> that belongs to the int sourceItem.Key. In the parameter resultSelector you get a combination of the complete sourceItem, with one item from the list:
(sourceItem, listItem) =>
So if your source is:
{ 1, {"A", "B"} }
{ 2, {"C", "D" "E"} }
{ 3, empty list }
You get:
( { 1, {"A", "B"} }, "A")
( { 1, {"A", "B"} }, "B")
( { 2, {"C", "D" "E"} }, "C")
( { 2, {"C", "D" "E"} }, "D")
( { 2, {"C", "D" "E"} }, "E")
No items for 3, the list is empty
Now, from every sourceItem you want sourceItem.Key.ToString(), from every listItem you want the complete listItem. So your SelectMany will be:
var results = source.SelectMany(sourceItem => sourceItem.Value,
(sourceItem, listItem) => new KeyValuePair<string, string>
(sourceItem.Key.ToString, listItem))
.ToList();
So what I am trying to do is order a dictionary(dict2) based off of another dictionary's(dict1) ordering based off of its Key; The two dictionaries have the same Values but not the same keys.
There is a graph below to visualize what I am trying to do.
enter image description here
You can use Linq to order one dictionary by the index of it's value in the other dictionary. There is probably a shorter way to do it, but this should work:
var dict1 = new Dictionary<int, string>
{
{12, "hello"},
{67, "green"},
{29, "blue"},
{15, "red"},
{40, "house"}
};
var dict2 = new Dictionary<string, string>
{
{"tree", "green"},
{"person", "hello"},
{"car", "red"},
{"floor", "red"},
{"dirt", "green"},
};
var ordered = dict2
.OrderBy(d2Item => dict1.FirstOrDefault(d1Item => d1Item.Value == d2Item.Value).Key)
.ToDictionary(item => item.Key, item => item.Value);
I am new to C#. I have an array of lists that looks something like this:
var baskets = [
[apples, oranges, peaches],
[oranges, grapes, bananas],
[oranges, grapes, apples]
[bananas, strawberries, peaches]
]
I need to turn it into a single array with a count of each fruit like this:
var fruitCount = [
{fruit: apples , count:2},
{fruit: oranges, count: 3},
{fruit: peaches, count: 2},
{fruit: grapes, count: 2},
{fruit: bananas, count: 2},
{fruit: strawberries, count: 1}]
I was looking at LINQ's ".SelectMany" but it just seems to flatten out the array into one list. I honestly don't know how to begin. Can anyone point me to a code sample that could help?
Try this:
var result = baskests.SelectMany(x => x)
.GroupBy(x => x)
.Select(x => new {
Fruit = x.Key,
Count = x.Count()
});
This does exactly what Rahul suggested in the comment. It first flattens all fruits into one single list containing duplicates and than groups the list. Finally the Select-statement will create an anonymous instance for every group having a Fruit- and a Count-property.
You need to flatten the array with SelectMany and then group the entries:
var flattened = baskets.SelectMany(basket => basket);
var fruitCount = flattened.GroupBy(fruit => fruit,
(fruit, g) => new { fruit, count = g.Count()});
Suppose we have a
var dictionary= new Dictionary<int, IList<int>>();
What I want is to ouput a sorted version of it, ordered first by keys and then by values inside a list.
E.g.
1 2, 1, 6
5 2, 1
2 1, 3
Becomes
1 1, 2, 6
2 1, 3
5 1, 2
I tried doing it inside foreach, but obviously this is a bad idea to change the thing you are iterating.
Try this:
// Creating test data
var dictionary = new Dictionary<int, IList<int>>
{
{ 1, new List<int> { 2, 1, 6 } },
{ 5, new List<int> { 2, 1 } },
{ 2, new List<int> { 2, 3 } }
};
// Ordering as requested
dictionary = dictionary
.OrderBy(d => d.Key)
.ToDictionary(
d => d.Key,
d => (IList<int>)d.Value.OrderBy(v => v).ToList()
);
// Displaying the results
foreach(var kv in dictionary)
{
Console.Write("\n{0}", kv.Key);
foreach (var li in kv.Value)
{
Console.Write("\t{0}", li);
}
}
A Dictionary is unsorted. To sort a dictionary you can use the OrderedDictionary.
To sort the lists, you can use List<T>.OrderBy()
You can use LINQ to order the contents of the dictionary like this:
var dictionary = new Dictionary<int, IList<int>>();
var orderedItems = dictionary
.OrderBy(pair => pair.Key)
.Select(new {
Key = pair.Key,
Value = pair.Value.OrderBy(i => i)});
Of course, this is rather ugly. A better option at this point is to use LINQ syntax
var orderedItems =from pair in dictionary
orderby pair.Key
let values = pair.Value.OrderBy(i => i)
select new { Key = pair.Key, Value = values };
If you need to use the resulting IEnumerable as a list or array, you can create one using ToList or ToArray. In most cases though, you can just use the IEnumerable as it is
You can loop through the dictionary items and sort each list seperately. it will look like this:
SortDictionary(dictionary);
after that:
foreach (System.Collections.Generic.KeyValuePair<int,IList<int>> list in dictionary)
{
SortDictionary( list.Value)
}
I have the following dictionary:
Dictionary<int, string> selectedDrivers = new Dictionary<int, string>()
{
{ 1, "Michael Schumacher" },
{ 2, "Michael Schumacher" },
{ 3, "Jensen Button" }
};
What I try to achieve is a linq query that will find the duplicates, retrieve the name only once, along with the positions this duplicate has. So, for example, the above would result in "Michael Schumacher" 1 2. I would like the result to go into a Dictionary<string, List<int>>.
Getting excited fast, this little nugget I wrote seems to be going in the right direction, except that I have Michael Schumacher twice. And it's not yet in a Dictionary<string, List<int>>
var a = selectedDrivers.GroupBy(a => a.Value).
Where(b => b.Count() > 1);
var a = selectedDrivers.GroupBy(a=>a.Value)
.Where(g=>g.Count() > 1)
.ToDictionary(g => g.Key, g => g.Select(a=>a.Key).ToList());