Reputation: 35
I am having difficulty combining two dictionaries into a dictionary with two values combined to a list for identical keys. For example, having D1 and D2
D1 = {2:"a",
3:"b",
4: "c"}
D2 = {1:"e",
2:"f",
4:"h",
5:"i"}
I would like to create D3.
D3= { 1:["", "e"]
2:["a", "f"]
3:["b", ""]
4:["c":"h"]
5:["", "i"]}
Thank you.
Upvotes: 0
Views: 888
Reputation: 11
Please see, here is another approach for this query -
Input -
Dictionary<int, string> first_dict = new Dictionary<int, string>()
{
{ 2,"a" },
{ 3,"b" },
{ 4, "c"}
};
Dictionary<int, string> second_dict = new Dictionary<int, string>()
{
{ 1,"e" },
{ 2,"f" },
{ 4, "h"},
{ 5, "i"}
};
First, I got common keys from both dictionaries like this -
var allKeys = first_dict.Concat(second_dict).OrderBy(b => b.Key).Select(b => b.Key).Distinct().ToList();
and then I created two another dictionaries and inserted data into them like this -
Dictionary<int, string> first_dict_res = new Dictionary<int, string>();
Dictionary<int, string> second_dict_res = new Dictionary<int, string>();
foreach (var keyItem in allKeys)
{
var first_dict_res_value = (first_dict.ContainsKey(keyItem)) ? first_dict[keyItem] : null;
first_dict_res.Add(keyItem, first_dict_res_value);
var second_dict_res_value = (second_dict.ContainsKey(keyItem)) ? second_dict[keyItem] : null;
second_dict_res.Add(keyItem, second_dict_res_value);
}
and then I concatenated the result from both dictionaries to get the desired result-
var res_dict = first_dict_res.Concat(second_dict_res).GroupBy(b => b.Key)
.Select(c => new { key = c.Key, values = string.Join(",", c.Select(b => b.Value)) }).ToList();
Upvotes: 0
Reputation: 155726
This can be done in a single Linq expression like so:
d1
and d2
to a single flat sequence of (Int32,String)
value-tuples.Int32
key (this is the main step).Dictionary<Int32,String> d1 = new Dictionary<Int32,String>()
{
{ 2, "a" },
{ 3, "b" },
{ 4, "c" },
};
Dictionary<Int32,String> d2 = new Dictionary<Int32,String>()
{
{ 1, "e" },
{ 2, "f" },
{ 4, "h" },
{ 5, "i" },
};
Dictionary<Int32,List<String>> d3 = Array
.Empty<( Int32 k, String v )>()
// Step 1:
.Concat( d1.Select( kvp => ( k: kvp.Key, v: kvp.Value ) ) )
.Concat( d2.Select( kvp => ( k: kvp.Key, v: kvp.Value ) ) )
// Step 2:
.GroupBy( t => t.k )
// Step 3:
.ToDictionary(
grp => grp.Key,
grp => grp.Select( t => t.v ).OrderBy( v => v ).ToList()
);
An advantage of this approach is that it works for any number of duplicated values (not just two). Also, the use of ValueTuple
means this approach should have fewer heap-allocations.
Screenshot proof of it working in LinqPad:
The expression can be made more succint - I use a more verbose style myself, but if you want to be cryptic about it by re-using KeyValuePair
instead of ValueTuple
, and if you don't care about ordering, then you can do this:
var d3 = d1
.Concat( d2 )
.GroupBy( kvp => kvp.Key )
.ToDictionary( g => g.Key, g => g.Select( kvp => kvp.Value ).ToList() );
Upvotes: 2
Reputation: 81593
This doesn't need another answer the others answers are plenty good enough and well done, however here is another (convoluted) approach
Given
var d1 = new Dictionary<int, string> {{2, "a"}, {3, "b"}, {4, "c"}};
var d2 = new Dictionary<int, string> { { 1, "e" }, { 2, "f" }, { 4, "h" }, { 5, "i" } };
Usage
static string[] Stuff((string, string)[] v) =>
new[] {v[0].Item1 ?? v.ElementAtOrDefault(1).Item1 ?? "", v[0].Item2 ?? v.ElementAtOrDefault(1).Item2 ?? "" };
var result = d1
.Select(x => (x.Key, (x.Value,(string)null)))
.Concat(d2.Select(x => (x.Key, ((string)null, x.Value ))))
.GroupBy(element => element.Key)
.ToDictionary(x => x.Key, x => Stuff(x.Select(y =>y.Item2).ToArray()))
Output
foreach (var item in result.OrderBy(x => x.Key))
Console.WriteLine($"{item.Key}: {string.Join(",", item.Value)}");
---
1: ,e
2: a,f
3: b,
4: c,h
5: ,i
Upvotes: 0
Reputation: 1438
Simplest solution would be with Dictionary.Keys
var D1 = new Dictionary<int,string>(){{2,"a"}, {3,"b"},{4,"c"}};
var D2 = new Dictionary<int,string>(){{1,"e"},{2,"f"}, {4,"h"},{5,"i"}};
var keys = D1.Keys.Union(D2.Keys).OrderBy(key => key);
var test = keys.Select(key => new {Key = key, Value= new string[] {D1.ContainsKey(key) ? D1[key] : "", D2.ContainsKey(key) ? D2[key] : ""} });
Console.WriteLine(test);
Interactive: https://rextester.com/UXQ51844
Alternatively, you could do something similar to this: LINQ - Full Outer Join
Upvotes: 1
Reputation: 74740
I think this is simpler without LINQ (LINQ is a hammer, not every problem is a nail)
Let's loop from 1 to 5, putting a new List for each int. The list is inited with d1's value and d2's value
var d3 = new Dictionary<int, List<string>>();
for(int x=1;x<6;x++)
d3[x] = new() { d1.GetValueOrDefault(x,""), d2.GetValueOrDefault(x,"") };
If your ints aren't always contiguous you could (use a bit of LINQ 😀 and..)
foreach(int x in d1.Keys.Union(d2.Keys))
d3[x] = new() { d1.GetValueOrDefault(x,""), d2.GetValueOrDefault(x,"") };
Upvotes: 0
Reputation: 45109
Sounds to be a job for LINQ. Here is one possibility to solve this issue:
public class Element
{
public int Index { get; set; }
public string Value { get; set; }
}
public class GroupedElement
{
public int Index { get; set; }
public IReadOnlyList<string> Values { get; set; }
}
public static class Program
{
public static void Main(string[] args)
{
var d1 = new[]
{
new Element { Index = 2, Value = "a" },
new Element { Index = 3, Value = "b" },
new Element { Index = 4, Value = "c" },
};
var d2 = new[]
{
new Element { Index = 1, Value = "e" },
new Element { Index = 2, Value = "f" },
new Element { Index = 4, Value = "h" },
new Element { Index = 5, Value = "i" },
};
var result = d1.Concat(d2)
.GroupBy(element => element.Index)
.Select(group => new GroupedElement { Index = group.Key, Values = group.Select(g => g.Value).ToList() })
.ToList();
foreach (var item in result)
{
Console.WriteLine($"{item.Index}: {string.Join(",", item.Values)}");
}
}
}
Upvotes: 1