This is 2D array:
int[][] array2D = new int[7][];
for (int i = 0; i < 7; i++)
array2D[i] = new int[7];
How can I turn the following into a LINQ query, or use enumerable methods to achieve the same output?
var lst = new List<Point>();
for (int r = 0; r < array2D.Length; r++)
for (int c = 0; c < array2D[r].Length; c++)
if (array2D[r][c] == 0)
lst.Add(new Point(c, r));
EDIT - Solution based on #'King King's answer
var lst = m_boardArr.SelectMany((row, rowIndex) =>
row.Select((val, colIndex) =>
new { val, point = new Point(colIndex, rowIndex) })
.Where(col => col.val == 0)
.Select(col => col.point)).ToList();
Try this:
var lst = array2D.SelectMany((x,r) => x.Select((a,c)=> new {a,b=new Point(c,r)})
.Where(a=>a.a==0)
.Select(a=>a.b)).ToList();
The trick is to use the Select and SelectMany that capture the loop variables into an anonymous type, then get those properties back later after the Where clause, thus:
var list = array2D
.SelectMany((row, r) => row
.Select((el, c) =>
new {Element = el, ColIndex = c, RowIndex = r})
.Where(thing => thing.Element == 0)
.Select(thing => new Point(thing.RowIndex, thing.ColIndex)))
.ToList();
EDIT: Bartosz's comment applies to this solution as well. Unreadable!
var lst = array2D
.SelectMany((innerArray, r)
=> Enumerable
.Range(0, innerArray.Length)
.Where(c => innerArray[c] == 0)
.Select(c => new Point(c, r)))
.ToList();
However, your current solution is more readable.
Related
When i have a list
IList<int> list = new List<int>();
list.Add(100);
list.Add(200);
list.Add(300);
list.Add(400);
list.Add(500);
What is the way to extract a pairs
Example : List elements {100,200,300,400,500}
Expected Pair : { {100,200} ,{200,300} ,{300,400} ,{400,500} }
The most elegant way with LINQ: list.Zip(list.Skip(1), Tuple.Create)
A real-life example: This extension method takes a collection of points (Vector2) and produces a collection of lines (PathSegment) needed to 'join the dots'.
static IEnumerable<PathSegment> JoinTheDots(this IEnumerable<Vector2> dots)
{
var segments = dots.Zip(dots.Skip(1), (a,b) => new PathSegment(a, b));
return segments;
}
This will give you an array of anonymous "pair" objects with A and B properties corresponding to the pair elements.
var pairs = list.Where( (e,i) => i < list.Count - 1 )
.Select( (e,i) => new { A = e, B = list[i+1] } );
You can use a for loop:
var pairs = new List<int[]>();
for(int i = 0; i < list.Length - 1; i++)
pairs.Add(new [] {list[i], list[i + 1]);
You can also use LINQ, but it's uglier:
var pairs = list.Take(list.Count - 1).Select((n, i) => new [] { n, list[i + 1] });
EDIT: You can even do it on a raw IEnumerable, but it's much uglier:
var count = list.Count();
var pairs = list
.SelectMany((n, i) => new [] { new { Index = i - 1, Value = n }, new { Index = i, Value = n } })
.Where(ivp => ivp.Index >= 0 && ivp.Index < count - 1) //We only want one copy of the first and last value
.GroupBy(ivp => ivp.Index, (i, ivps) => ivps.Select(ivp => ivp.Value));
More general would be:
public static IEnumerable<TResult> Pairwise<TSource, TResult>(this IEnumerable<TSource> values, int count, Func<TSource[], TResult> pairCreator)
{
if (count < 1) throw new ArgumentOutOfRangeException("count");
if (values == null) throw new ArgumentNullException("values");
if (pairCreator == null) throw new ArgumentNullException("pairCreator");
int c = 0;
var data = new TSource[count];
foreach (var item in values)
{
if (c < count)
data[c++] = item;
if (c == count)
{
yield return pairCreator(data);
c = 0;
}
}
}
Following solution uses zip method. Zip originalList and originalList.Skip(1) so that one gets desired result.
var adjacents =
originalList.Zip(originalList.Skip(1),
(a,b) => new {N1 = a, N2 = b});
Using .Windowed() from MoreLINQ:
var source = new[] {100,200,300,400,500};
var result = source.Windowed(2).Select(x => Tuple.Create(x.First(),x.Last()));
Off the top of my head and completely untested:
public static T Pairwise<T>(this IEnumerable<T> list)
{
T last;
bool firstTime = true;
foreach(var item in list)
{
if(!firstTime)
return(Tuple.New(last, item));
else
firstTime = false;
last = item;
}
}
I have Table like ProductInventory , In that I have some product with quantity .
I want select all rows where The least of a field equals to my input(number) .
I try with this :
List<product> Products = new List<product> {
new product{Id=1,Name="A",Quantity=1},
new product{Id=1,Name="A",Quantity=2},
new product{Id=1,Name="A",Quantity=3},
new product{Id=1,Name="B",Quantity=4},
new product{Id=1,Name="B",Quantity=7}
};
var result = Products
.AsEnumerable()
.GroupBy(r => r.Name)
.Where(g => (int)g.Sum(r =>r.Quantity)<= 4)
.ToList();
but it causes a return zero.
example:
I don't know is it possible in linq or not. But you can try this.
var result = Products.AsEnumerable().Where(g => g.Name == "A").ToList();
int userInput =4;
var total = 0;
var selectList = new List<product>();
for (int i = 0; i < result.Count; i++)
{
for (int j = i; j < result.Count; j++)
{
if (total + result[j].Quantity <= userInput)
{
total += result[j].Quantity;
selectList.Add(result[j]);
}
}
if (total == userInput)
break;
else
{
total = 0;
selectList = new List<product>();
}
}
if(userInput!=total)
selectList = new List<product>();
With that latest update, I think I finally understand what you are trying to do.
This won't work however, because you cant build the sum of booleans.
var result = Products
.AsEnumerable()
.GroupBy(r => r.Name)
.Where(g => g.Sum(r =>r.Quantity== 4))
.ToList();
What you actually want is
var result = Products
.GroupBy(r => r.Name)
.Where(g => g.Sum(r =>r.Quantity) >= 4) //or == 4 or whatever
.ToList();
Say I have an array like this
string [] fruits = {"watermelon","apple","apple","kiwi","pear","banana"};
Is there an built in function that allows me to query all the index of "apple" ?
For example,
fruits.FindAllIndex("apple");
will return an array of 1 and 2
If there is not, how should I implement it?
Thanks!
LINQ version:
var indexes = fruits.Select((value, index) => new { value, index })
.Where(x => x.value == "apple")
.Select(x => x.index)
.ToList();
Non-LINQ version, using Array<T>.IndexOf() static method:
var indexes = new List<int>();
var lastIndex = 0;
while ((lastIndex = Array.IndexOf(fruits, "apple", lastIndex)) != -1)
{
indexes.Add(lastIndex);
lastIndex++;
}
One way would be to write like this:
var indices = fruits
.Select ((f, i) => new {f, i})
.Where (x => x.f == "apple")
.Select (x => x.i);
Or the traditional way:
var indices = new List<int>();
for (int i = 0; i < fruits.Length; i++)
if(fruits[i] == "apple")
indices.Add(i);
Pretty easy with an extension method.
var fruits = new[] { "watermelon","apple","apple","kiwi","pear","banana" };
var indexes = fruits.FindAllIndexes("apple");
public static class Extensions
{
public static int[] FindAllIndexes(this string[] array, string search) => array
.Select((x, i) => (x, i))
.Where(value => value.x == search)
.Select(value => value.i)
.ToArray();
}
I have a list that contains 8 elements:
ConfigFile.ControllerList
this list is type of:
List<Controller>
How can i add Controllers from ControllerList to 3 dictionary keys. Dictionary is like:
Dictionary<int, List<Controller>> ControllerDictionary = new Dictionary<int, List<Controller>>();
I want to add first 3 controllers to dictionary key 0, then want to add next 3 controllers to dictionary key 1 and lastly want to add last 2 controllers to dictionary key 2. How can i do that?
You can use / to split the list into sub-list:
var ControllerDictionary = ControllerList
.Select((c, i) => new { Controller = c, Index = i })
.GroupBy(x => x.Index / maxGroupSize)
.Select((g, i) => new { GroupIndex = i, Group = g })
.ToDictionary(x => x.GroupIndex, x => x.Group.Select(xx => xx.Controller).ToList());
The idea is to first group the elements by indexes, then divide them by an int maxGroupSize(in your case 3). Then convert each group to a list.
Not sure if there's a more elegant solution, but something like this should work:
var dict = new Dictionary<int, List<Controller>>();
int x = 0;
while (x < controllerList.Count)
{
var newList = new List<Controller> { controllerList[x++] };
for (int y = 0; y < 2; y++) // execute twice
if (x < controllerList.Count)
newList.Add(controllerList[x++]);
dict.Add(dict.Count, newList);
}
To make it more general, you could also create newList empty to start, and then change y < 2 to y < GROUP_SIZE where GROUP_SIZE is whatever sized groups you want. Could even then extract this to an extension method:
public static Dictionary<int, List<T>> ToGroupedDictionary<T>
(this IList<T> pList, int pGroupSize)
{
var dict = new Dictionary<int, List<T>>();
int x = 0;
while (x < pList.Count)
{
var newList = new List<T>();
for (int y = 0; y < pGroupSize && x < pList.Count; y++, x++)
newList.Add(pList[x]);
dict.Add(dict.Count, newList);
}
return dict;
}
And then you can do this:
var groups = new[]
{
"Item1",
"Item2",
"Item3",
"Item4",
"Item5",
"Item6",
"Item7",
"Item8"
}.ToGroupedDictionary(3);
I have an array of 2000 strings. The strings are: "art", "economy", "sport" and "politic". I want to group each 500 elements and get their counts
Could anyone help please?
Another solution:
var count = 0;
var dictionaries =
strings.GroupBy(s => count++ / 500)
.Select(g => g.Distinct().ToDictionary(k => k, k => g.Count(s => s == k)))
.ToList();
This will create a List<Dictionary<string, int>>. Each dictionary represents a tally of 500 elements (or possibly less for the last dictionary), where the keys are strings and the values are the number of occurrences of the string among the 500 elements the dictionary represents.
There is no requirement to hardcode all the possible values that may be encountered.
For the maximum possible performance you can also use this version:
var count = 0;
var dictionaries =
strings.GroupBy(s => count++ / 500)
.Select(g => g.Aggregate(
new Dictionary<string, int>(),
(d, w) => { d[w] = (d.ContainsKey(w) ? d[w] + 1 : 1); return d; })
)
.ToList();
This version iterates over each element in your source array exactly once. The output is in the same format as the first version.
var result = strings.Select((s, i) => new { s, i })
.GroupBy(x => x.i / 500)
.Select(x => x.GroupBy(y => y.s)
.Select(z => new {
Name=z.Key,
Count=z.Count()
}).ToList())
.ToList();
Try
var grouping = Enumerable.Range(0,2000)
.Select(i => i / 500)
.Zip(Strings, (i,s) => new { Group = i, Str = s})
.GroupBy(anon => anon.Group,
anon => anon.Str,
(key,g) => new
{
Key = key,
Art = g.Count(str => str == "art"),
Economy = g.Count(str => str == "economy"),
Politic = g.Count(str => str == "politic"),
Sport= g.Count(str => str == "sport")
});
foreach(anon in grouping)
{
//textbox logic OP will have to change to suit
TextBox1.WriteLine(String.Format("Group: {0}", anon.Key));
TextBox1.WriteLine(String.Format("Art: {0}",anon.Art));
TextBox1.WriteLine(String.Format("Economy: {0}",anon.Economy ));
TextBox1.WriteLine(String.Format("Politic: {0}",anon.Politic ));
TextBox1.WriteLine(String.Format("Sport: {0}",anon.Sport));
}
Alternatively (as per Snowbear)
var grouping = Strings.Select((s,i) => new { Group = i / 500, Str = s})
.GroupBy(anon => anon.Group,
anon => anon.Str,
(key,g) => new
{
Key = key,
Art = g.Count(str => str == "art"),
Economy = g.Count(str => str == "economy"),
Politic = g.Count(str => str == "politic"),
Sport= g.Count(str => str == "sport")
});
foreach(anon in grouping)
{
//textbox logic OP will have to change to suit
TextBox1.WriteLine(String.Format("Group: {0}",anon.Key + 1));
TextBox1.WriteLine(String.Format("Art: {0}",anon.Art));
TextBox1.WriteLine(String.Format("Economy: {0}",anon.Economy ));
TextBox1.WriteLine(String.Format("Politic: {0}",anon.Politic ));
TextBox1.WriteLine(String.Format("Sport: {0}",anon.Sport));
}
int CountElementsInGroup = 500;
//from 500 to 1000
int NumberGroup = 2;
string[] GroupTypes = new string[4] { "art", "economy", "sport", "politic" };
//Fill example array
string[] arr = new string[2000];
Random rand = new Random();
for (int i = 0; i < arr.Length;i++ )
arr[i] = GroupTypes[rand.Next(0, 3)];
var res = (from p in arr.Skip((NumberGroup - 1) * CountElementsInGroup).Take(CountElementsInGroup)
group p by p into g
select new GroupCountClass { GroupName = g.Key, GroupCount = g.Count() });
textBox1.Text = "";
foreach (GroupCountClass c in res)
{
textBox1.Text += String.Format("GroupName:{0} Count:{1};",c.GroupName,c.GroupCount);
}