Develop Reference

Create a sliding window from a list

I need to iterate over a list while getting the next and previous Items. I'm currently doing it like so:
var items = collection.ToList();
for (int index = 0; index < items.Count; index++)
{
var prevItem = index == 0 ? null : items[index - 1];
var currentItem = items[index];
var nextItem = (index + 1) == items.Count ? null : items[index + 1];
// do work
}
This work but it is not as nice and readable as I would like. Is there a more readable way of creating a sliding window? which doesn't involve all of the ugly ternary checks. I feel like there is a more friendly way using select, skip, take, and default if empty

This sort of problem is best solved using generators if you want it to be reusable IMHO.
public static IEnumerable<(T PrevItem, T CurrentItem, T NextItem)>
SlidingWindow<T>(this IEnumerable<T> source, T emptyValue = default)
{
using (var iter = source.GetEnumerator())
{
if (!iter.MoveNext())
yield break;
var prevItem = emptyValue;
var currentItem = iter.Current;
while (iter.MoveNext())
{
var nextItem = iter.Current;
yield return (prevItem, currentItem, nextItem);
prevItem = currentItem;
currentItem = nextItem;
}
yield return (prevItem, currentItem, emptyValue);
}
}
Then use it:
foreach (var (prevItem, currentItem, nextItem) in collection.SlidingWindow())
{
// do stuff with prevItem, currentItem, nextItem
}

Generic window size:
public IEnumerable<IEnumerable<T>> CreateSlidingWindow<T>(IEnumerable<T> input, int windowSize)
{
if (input == null || input.Count() < windowSize)
{
return new List<IEnumerable<T>>();
}
var first = new[] { input.Take(windowSize) };
var rest = CreateSlidingWindow(input.Skip(1), windowSize);
return first.Union(rest);
}

One way to make it more nicer is to transform your collection in a List of objects which contain the item, prevItem and nextItem:
static void Main(string[] args)
{
var collection = new List<string> { "A", "B", "C", "D", "E" };
var items = collection.Select((item, index) => new
{
Item = item,
PreVItem = index > 0 ? collection[index - 1] : null,
NextItem = index < collection.Count-1 ? collection[index + 1] : null
});
foreach (var item in items)
{
Console.WriteLine($"{item.PreVItem} \t {item.Item} \t {item.NextItem}");
}
Console.ReadLine();
}

Created the following solution that is using an enumerator.
public static IEnumerable<IList<T>> SlidingWindowValues<T>(this IEnumerable<T> source, int windowSize)
{
var windows = Enumerable.Range(0, windowSize)
.Select(_ => new List<T>())
.ToList();
int i = 0;
using (var iter = source.GetEnumerator())
{
while (iter.MoveNext())
{
var c = Math.Min(i + 1, windowSize);
for (var j = 0; j < c; j++)
{
windows[(i - j) % windowSize].Add(iter.Current);
}
if (i >= windowSize - 1)
{
var previous = (i + 1) % windowSize;
yield return windows[previous];
windows[previous] = new List<T>();
}
i++;
}
}
}

How to check if file contains strings, which will double repeat sign?

I would like to check if file containing some strings, separated with # contains double repeat sign. Example:
I have a file like this:
1234#224859#123567
I am reading this file and putting strings separated with # it into array.
I would like to find which strings have a digit repeated next to each other (in this case 224859) and return position of first digit that repeats in this string?
This is what I have so far:
ArrayList list = new ArrayList();
OpenFileDialog openFile1 = new OpenFileDialog();
int size = -1;
DialogResult dr = openFile1.ShowDialog();
string file = openFile1.FileName;
try
{
string text = File.ReadAllText(file);
size = text.Length;
string temp = "";
for (int i = 0; i < text.Length; i++)
{
if (text[i] != '#')
{
temp += text[i].ToString();
}
else
{
list.Add(temp);
temp = "";
}
}
}
catch (IOException)
{
}
string all_values = "";
foreach (Object obj in list)
{
all_values += obj.ToString() + " => ";
Console.WriteLine(" => ", obj);
}
textBox1.Text = (all_values);

This regex should do the trick.
var subject = "1234#224859#123567";
foreach(var item in subject.Split('#'))
{
var regex = new Regex(#"(?<grp>\d)\k<grp>");
var match =regex.Match(item);
if(match.Success)
{
Console.WriteLine("Index : {0}, Item:{1}", match.Index, item);
//prints Index : 0, Item:224859
}
}

This is a more procedural approach than Sriram's, but the main benefit is remembering your results in order to use them later in your program.
Basically, the string is split based on the # delimiter, which returns a string[] which holds each number inside. Then, for each string you iterate through the characters and check to see if the current character at i matches the next character at i + 1. If so, the earliest appearance of a duplicate digit is at i, so i is remembered and we break out of the loop that processes chars.
Since int is a non-nullable type, I decided to use -1 to indicate that a match was not found in a string.
Dictionary<string, int> results = new Dictionary<string, int>();
string text = "1234#224859#123567#11#4322#43#155";
string[] list = text.Split('#');
foreach (string s in list)
{
int tempResult = -1;
for (int i = 0; i < s.Length - 1; i++)
{
if(s.ElementAt(i) == s.ElementAt(i + 1))
{
tempResult = i;
break;
}
}
results.Add(s, tempResult);
}
foreach (KeyValuePair<string, int> pair in results)
{
Console.WriteLine(pair.Key + ": " + pair.Value);
}
Output:
1234: -1
224859: 0
123567: -1
11: 0
4322: 2
43: -1
155: 1

here's another Regex that works
int indexof = -1;
String input = "3492883#32280948093284#990303294";
string[] numbers = input.Split('#');
foreach(string n in numbers)
{
Match m=Regex.Match(n, #"(\d)\1+");
if (m.Success)
{
indexof = m.Index;
}
}

Would this do what you are looking for?
string text = File.ReadAllText(file);
string[] list = text.Split(new char[] { '#' });
Then, after you have the strings separated:
foreach (string s in list)
{
int pos = HasDoubleCharacter(s);
if (pos > -1)
{
// do something
}
}
private static int HasDoubleCharacter(string text)
{
int pos = 0;
char[] c3 = text.ToCharArray();
char lastChar = (char)0;
foreach (char c in c3)
{
if (lastChar == c)
return pos;
lastChar = c;
pos++;
}
return -1;
}
Or are you just looking for the list of positions of all doubles in the original text. If so (and you don't need to act on the various strings separately, you might try this:
private static List<int> FindAllDoublePositions(string text)
{
List<int> positions = new List<int>();
char[] ca = text.ToCharArray();
char lastChar = (char)0;
for (int pos = 0; pos < ca.Length; pos++)
{
if (Char.IsNumber(ca[pos]) && lastChar == ca[pos])
positions.Add(pos);
lastChar = ca[pos];
}
return positions;
}

If your looking for a specific string pattern, Regex is most likely to be your best friend :
string text = "1234#224859#123567asdashjehqwjk4234#244859#123567asdhajksdhqjkw1434#244859#123567";
var results = Regex.Matches(text, #"\d{4}#(?<Value>\d{6})#\d{4}");
var allValues = "";
foreach (Match result in results)
{
allValues = result.Groups["Value"].Value + " => ";
Console.WriteLine(" => ", result.Value);
}

Concat arrays at a certain index with LINQ?

I want to do this in LINQ:
public static void ConcatAt(this string[] items, string[] others, int at)
{
for (int i = 0; i < others.Length && at < items.Length; i++, at++) {
items[at] = others[i];
}
}
Usage:
string[] groups = { "G1", "G2", "G3" };
string[] names = new string[groups.Length + 1];
names[0] = "Choose";
names.ConcatAt(groups, 1);
foreach (var n in names)
Console.WriteLine(n);
/*
Choose
G1
G2
G3
*/
String was just an example, could be anything though.
So is there a LINQ method that does this?
Doing a names = names.Concat(groups).ToArray(); will include the empty strings that's in names so if I print names I'd get:
/*
Choose
G1
G2
G3
*/
Thanks.

Why are you not using Array.Copy?
Array.Copy(groups, 0, names, at,groups.Length);

I think it will work for you
string[] groups = { "G1", "G2", "G3" };
var myNewItems = groups.ToList();
int pos = 1;
string value = "Choose";
myNewItems.Insert(pos,value);
foreach (var v in myNewItems)
{
Console.WriteLine(v);
}
Console.ReadLine();

How do I 'foreach' through a two-dimensional array?

I've got a two-dimensional array,
string[,] table = {
{ "aa", "aaa" },
{ "bb", "bbb" }
};
And I'd like to foreach through it like this,
foreach (string[] row in table)
{
Console.WriteLine(row[0] + " " + row[1]);
}
But, I get the error:
Can't convert type string to string[]
Is there a way I can achieve what I want, i.e. iterate through the first dimension of the array with the iterator variable returning me the one-dimensional array for that row?

Multidimensional arrays aren't enumerable. Just iterate the good old-fashioned way:
for (int i = 0; i < table.GetLength(0); i++)
{
Console.WriteLine(table[i, 0] + " " + table[i, 1]);
}

As others have suggested, you could use nested for-loops or redeclare your multidimensional array as a jagged one.
However, I think it's worth pointing out that multidimensional arrays are enumerable, just not in the way that you want. For example:
string[,] table = {
{ "aa", "aaa" },
{ "bb", "bbb" }
};
foreach (string s in table)
{
Console.WriteLine(s);
}
/* Output is:
aa
aaa
bb
bbb
*/

If you define your array like this:
string[][] table = new string[][] {
new string[] { "aa", "aaa" },
new string[]{ "bb", "bbb" }
};
Then you can use a foreach loop on it.

UPDATE: I had some time on my hands, so ... I went ahead and fleshed out this idea. See below for the code.
Here's a bit of a crazy answer:
You could do what you're looking for -- essentially treat a two-dimensional array as a table with rows -- by writing a static method (perhaps an extension method) that takes a T[,] and returns an IEnumerable<T[]>. This would require copying each "row" of the underlying table into a new array, though.
A perhaps better (though more involved) approach would be to actually write a class that implements IList<T> as a wrapper around a single "row" of a two-dimensional array (you would probably set IsReadOnly to true and just implement the getter for the this[int] property and probably Count and GetEnumerator; everything else could throw a NotSupportedException). Then your static/extension method could return an IEnumerable<IList<T>> and provide deferred execution.
That way you could write code pretty much like what you have:
foreach (IList<string> row in table.GetRows()) // or something
{
Console.WriteLine(row[0] + " " + row[1]);
}
Just a thought.
Implementation suggestion:
public static class ArrayTableHelper {
public static IEnumerable<IList<T>> GetRows<T>(this T[,] table) {
for (int i = 0; i < table.GetLength(0); ++i)
yield return new ArrayTableRow<T>(table, i);
}
private class ArrayTableRow<T> : IList<T> {
private readonly T[,] _table;
private readonly int _count;
private readonly int _rowIndex;
public ArrayTableRow(T[,] table, int rowIndex) {
if (table == null)
throw new ArgumentNullException("table");
if (rowIndex < 0 || rowIndex >= table.GetLength(0))
throw new ArgumentOutOfRangeException("rowIndex");
_table = table;
_count = _table.GetLength(1);
_rowIndex = rowIndex;
}
// I didn't implement the setter below,
// but you easily COULD (and then set IsReadOnly to false?)
public T this[int index] {
get { return _table[_rowIndex, index]; }
set { throw new NotImplementedException(); }
}
public int Count {
get { return _count; }
}
bool ICollection<T>.IsReadOnly {
get { return true; }
}
public IEnumerator<T> GetEnumerator() {
for (int i = 0; i < _count; ++i)
yield return this[i];
}
// omitted remaining IList<T> members for brevity;
// you actually could implement IndexOf, Contains, etc.
// quite easily, though
}
}
...now I think I should give StackOverflow a break for the rest of the day ;)

It depends on how you define your multi-dimensional array. Here are two options:
using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
// First
string[,] arr1 = {
{ "aa", "aaa" },
{ "bb", "bbb" }
};
// Second
string[][] arr2 = new[] {
new[] { "aa", "aaa" },
new[] { "bb", "bbb" }
};
// Iterate through first
for (int x = 0; x <= arr1.GetUpperBound(0); x++)
for (int y = 0; y <= arr1.GetUpperBound(1); y++)
Console.Write(arr1[x, y] + "; ");
Console.WriteLine(Environment.NewLine);
// Iterate through second second
foreach (string[] entry in arr2)
foreach (string element in entry)
Console.Write(element + "; ");
Console.WriteLine(Environment.NewLine);
Console.WriteLine("Press any key to finish");
Console.ReadKey();
}
}
}

Here's a simple extension method that returns each row as an IEnumerable<T>. This has the advantage of not using any extra memory:
public static class Array2dExt
{
public static IEnumerable<IEnumerable<T>> Rows<T>(this T[,] array)
{
for (int r = array.GetLowerBound(0); r <= array.GetUpperBound(0); ++r)
yield return row(array, r);
}
static IEnumerable<T> row<T>(T[,] array, int r)
{
for (int c = array.GetLowerBound(1); c <= array.GetUpperBound(1); ++c)
yield return array[r, c];
}
}
Sample usage:
static void Main()
{
string[,] siblings = { { "Mike", "Amy" }, { "Mary", "Albert" }, {"Fred", "Harry"} };
foreach (var row in siblings.Rows())
Console.WriteLine("{" + string.Join(", ", row) + "}");
}

string[][] table = { ... };

string[][] languages = new string[2][];
languages[0] = new string[2];
languages[1] = new string[3];
// inserting data into double dimensional arrays.
for (int i = 0; i < 2; i++)
{
languages[0][i] = "Jagged"+i.ToString();
}
for (int j = 0; j < 3; j++)
{
languages[1][j] = "Jag"+j.ToString();
}
// doing foreach through 2 dimensional arrays.
foreach (string[] s in languages)
{
foreach (string a in s)
{
Console.WriteLine(a);
}
}

Using LINQ you can do it like this:
var table_enum = table
// Convert to IEnumerable<string>
.OfType<string>()
// Create anonymous type where Index1 and Index2
// reflect the indices of the 2-dim. array
.Select((_string, _index) => new {
Index1 = (_index / 2),
Index2 = (_index % 2), // ← I added this only for completeness
Value = _string
})
// Group by Index1, which generates IEnmurable<string> for all Index1 values
.GroupBy(v => v.Index1)
// Convert all Groups of anonymous type to String-Arrays
.Select(group => group.Select(v => v.Value).ToArray());
// Now you can use the foreach-Loop as you planned
foreach(string[] str_arr in table_enum) {
// …
}
This way it is also possible to use the foreach for looping through the columns instead of the rows by using Index2 in the GroupBy instead of Index 1. If you don't know the dimension of your array then you have to use the GetLength() method to determine the dimension and use that value in the quotient.

I'm not a big fan of this method because of the memory usage involved, but if you use the arrays it produces, it isn't such a waste.
public static void ForEachRow<T>(this T[,] list, Action<int, T[]> action)
{
var len = list.GetLength(0);
var sub = list.GetLength(1);
T[] e;
int i, j;
for (i = 0; i < len; i++)
{
e = new T[sub];
for (j = 0; j < sub; j++)
{
e[j] = list[i, j];
}
action(i, e);
}
}
Implementation:
var list = new[,]{0x0, 0x1, 0x2, 0x4, 0x8};
list.ForEachRow((i, row) =>
{
for (var j = 0; j < row.Length; j++)
{
Console.WriteLine("[{0},{1}]: {2}", i, j, row[j]);
}
});
The other solution I found is less memory intensive, but will use more CPU, especially when the dimensions of the arrays' entries are larger.
public static void ForEachRow<T>(this T[,] list, Action<int, IEnumerable<T>> action)
{
var len = list.GetLength(0);
var sub = list.GetLength(1);
int i, j;
IEnumerable<T> e;
for (i = 0; i < len; i++)
{
e = Enumerable.Empty<T>();
for (j = 0; j < sub; j++)
{
e = e.Concat(AsEnumerable(list[i, j]));
}
action(i, e);
}
}
private static IEnumerable<T> AsEnumerable<T>(T add)
{
yield return add;
}
Implementation:
var list = new[,]{0x0, 0x1, 0x2, 0x4, 0x8};
list.ForEachRow((i, row) =>
{
var j = 0;
forrach (var o in row)
{
Console.WriteLine("[{0},{1}]: {2}", i, j, o);
++j;
}
});
As a whole, I find the first option to be more intuitive, especially if you want to access the produced array by its indexer.
At the end of the day, this is all just eye candy, neither methods should really be used in favour of directly accessing the source array;
for (var i = 0; i < list.GetLength(0); i++)
{
foreach (var j = 0; j < list.GetLength(1); j++)
{
Console.WriteLine("[{0},{1}]: {2}", i, j, list[i, j]);
}
}

Remember that a multi-dimensional array is like a table. You don't have an x element and a y element for each entry; you have a string at (for instance) table[1,2].
So, each entry is still only one string (in your example), it's just an entry at a specific x/y value. So, to get both entries at table[1, x], you'd do a nested for loop. Something like the following (not tested, but should be close)
for (int x = 0; x < table.Length; x++)
{
for (int y = 0; y < table.Length; y += 2)
{
Console.WriteLine("{0} {1}", table[x, y], table[x, y + 1]);
}
}

I try this. I hope to help. It work with
static void Main()
{
string[,] matrix = {
{ "aa", "aaa" },
{ "bb", "bbb" }
};
int index = 0;
foreach (string element in matrix)
{
if (index < matrix.GetLength(1))
{
Console.Write(element);
if (index < (matrix.GetLength(1) - 1))
{
Console.Write(" ");
}
index++;
}
if (index == matrix.GetLength(1))
{
Console.Write("\n");
index = 0;
}
}

Shift elements in string array to left to fill 'holes'

I have a list of names and phone numbers like so:
var phonelist = List<string[]>
{
new string[] {"Bill", "1234", "12345", "12314" },
new string[] {"Bob", "", "12345", "12314" },
new string[] {"Chris", "", "", "12314" },
new string[] {"Dave", "1234", "", "12314" },
new string[] {"Andy", "1234", "12345", "" },
}
What is the most efficient/elegant way to process this list so that the 'empty' numbers get filled from the right ?
Note, the arrays should stay the same length, like so:
var phonelist = List<string[]>
{
new string[] {"Bill", "1234", "12345", "12314" },
new string[] {"Bob", "12345", "12314", "" },
new string[] {"Chris", "12314", "", "" },
new string[] {"Dave", "1234", "12314", "" },
new string[] {"Andy", "1234", "12345", "" },
}

for each array cell, check if its empty and swap it with cell+1, if it's still empty swap it with cell+2.. when cell becomes not empty do the same thing with cell+2...
int j;
foreach (string[] strs in phoneList)
{
for (int i = 0; i < strs.Length; i++)
{
j = 1;
while (string.IsNullOrEmpty(strs[i]) && j < strs.Length - i)
{
if (!string.IsNullOrEmpty(strs[i + j])) // to not swap 2 empty strings
{
strs[i] = strs[i + j];
strs[i + j] = "";
}
j++;
}
}
}

public static void PutEmptyStringsToTheEnd(string[] array) {
int j = 0;
for (int i = 0; i < array.Length; ++i)
if (array[i].Length > 0)
array[j++] = array[i];
while (j < array.Length)
array[j++] = "";
}
Call this function for each List element.

simple and ugly :(
for(var x=0;x<phonelist.Count;x++)
{
var strings = phonelist[x];
var l = strings.Length;
var newAr=new string[l];
var k = 0;
for (var i = 0; i < l; )
{
if(strings[i]!="")
{
newAr[k++] = strings[i];
}
i++;
}
for (; k < l; k++)
newAr[k] = "";
phonelist[x] = newAr;
}

You could do something like that :
Comparison<string> comparison = (x,y) =>
{
if (String.IsNullOrEmpty(x))
return 1;
if (String.IsNullOrEmpty(y))
return -1;
return String.Compare(x,y);
}
foreach (string[] array in phoneList)
{
Array.Sort(array, comparison);
}
However you will need to tune the comparison logic a bit to keep the names before the numbers
EDIT : since the name seems to always be the first element, another option is to exclude it from the sort. No Array.Sort overload takes a Comparison<T> and a range, so you have to use a IComparer<T> instead :
class MyComparer : IComparer<string>
{
public int Compare(string x, string y)
{
if (String.IsNullOrEmpty(x))
return 1;
if (String.IsNullOrEmpty(y))
return -1;
return String.Compare(x,y);
}
}
foreach (string[] array in phonelist)
{
Array.Sort(array, 1, array.Length - 1, new MyComparer());
}

This should work. I'm not that knownledged at C#, but the idea is there
foreach(string[] person in phonelist)
{
string[] newPerson = {"","","",""};
int index = 0;
for(int i=0; i<4; i++)
{
if(!String.IsNullOrEmpty(person[i])) newPerson[index++] = person[i];
}
person = newPerson;
}

This is cooler
List<string[]> result = phonelist.Select(per => per.OrderBy(txt=>txt.Length==0).ToArray()).ToList();

List<string[]> sorted = new List<string[]>();
foreach (string[] entry in phoneList)
{
List<string> nonEmpty = (from s in entry
where String.IsNullOrEmpty(s) == false
select s).ToList();
int pad = entry.Length - nonEmpty.Count;
List<string> pads = new List<string>();
while (pad > 0)
{
pads.Add(String.Empty);
--pad;
}
List<string> sortedEntry = new List<string>();
sortedEntry.AddRange(nonEmpty);
sortedEntry.AddRange(pads);
sorted.Add(sortedEntry.ToArray());
}