How to get a column of a 2D array in C#? - c#

var array = new[] {new[]{'a', 'b', 'c'}, new[]{'d', 'e', 'f'}, new[]{'g', 'h', 'i'}};
var column = // should be like new[]{'b', 'e', 'h'} given index 1
How to do this?
Of course I could create a new list, populate it manually iterating through all the lines in a loop and convert it to an array but Isn't there a more laconic way?

LINQ is your friend.
It's what separates us C# developers from the mere mortals.
var array = new[] { new[] { "a", "b", "c" }, new[] { "d", "e", "f" }, new[] { "g", "h", "i" } };
var col1 = array.Select(x => x[1]);
//col1 contains "b", "e" and "h"

You can write an extension method for that:
public static T[] GetColumn<T>(this T[][] source, int columnIndex)
{
int length = source.Length;
var values = new T[length];
for (int i = 0; i < length; i++)
{
if(source[i].Length > columnIndex)
values[i] = source[i][columnIndex];
}
return values;
}
Then :
var column = array.GetColumn(1);
This also doesn't throw an IndexOutOfRange exception if one of your arrays contains less element than column number.

Related

How do i loop string array in c# more than once?

I can't quite figure it out how to loop through string array after the first initial loop has been done.
My code right now is:
string[] assignments = new string[] {"A", "B", "C", "D", "E", "F"};
Array.Resize<string>(ref assignments, 99);
for (int i = 0; i < 99; i++)
{
Console.WriteLine(assignments[i]);
}
However, it seems that Resizing the array doesn't accomplish much, since arrays values after the 6th value is non-existant.
I need it to keep looping more then once:
A
B
C
D
E
F A
B
C
D
E
F ... and so on, until the limit of 99 is reached.
Use the mod operator.
string[] assignments = new string[] {"A", "B", "C", "D", "E", "F"};
for (int i = 0; i < 99; i++)
{
Console.WriteLine(assignments[i % assignments.Length]);
}
.net fiddle
You can use the modulus operator which "computes the remainder after dividing its first operand by its second."
void Main()
{
string[] assignments = new string[] {"A", "B", "C", "D", "E", "F"};
for (int i = 0; i < 99; i++)
{
var j = i % 6;
Console.WriteLine(assignments[j]);
}
}
0 % 6 = 0
1 % 6 = 1
...
6 % 6 = 0
7 % 6 = 1
... etc.
The obligatory LINQ solution, this extension comes in handy:
public static IEnumerable<T> RepeatIndefinitely<T>(this IEnumerable<T> source)
{
while (true)
{
foreach (var item in source)
{
yield return item;
}
}
}
Now your task is very easy and readable:
var allAssignments = assignments.RepeatIndefinitely().Take(99);
You can use a foreach-loop with Console.WriteLine or build a string:
string result1 = string.Concat(allAssignments);
string result2 = string.Join(Environment.NewLine, allAssignments)
How about using mod
string[] assignments = new string[] { "A", "B", "C", "D", "E", "F" };
for (int i = 0; i < 99; i++)
{
Console.WriteLine(assignments[i%6]);
}

Moving specific elements after others but not to top or bottom

Assume I have an array of
{ "w", "w", "z", "a", "c", "r", "f", "d", "e", "c", "g", "f", "m", "z" }
and I have a rule that all "c" should be moved before "f".
The goal to to keep as closest order to the original as possible while following the rule(s).
A real world example is a an app which knows that some plugin "A" should be higher than some plugin "B" in a load list.
So the expected result would be:
Moved c before first f:
{ "w", "w", "z", "a", "c", "r", "c"<<, "f", "d", "e", "g", "f", "m", "z" }
or
Moved f after last c:
{ "w", "w", "z", "a", "c", "r", "d", "e", "c", >>"f", "g", "f", "m", "z" }
Is it possible to use LINQ or anything ready for such purpose?
I tried OrderBy(x => x == "c" ? 0 : x == "f" ? 1 : (int?)null) but it moves elements to the end instead. I want to sort only specific elements with each other but keep their position relatively to other elements when possible.
UPDATE
The solution should work for any inputs:
public static char GetLetter(Random rand)
{
string chars = "abcdefghijklmnopqrstuvwxyz";
int num = rand.Next(0, chars.Length - 1);
return chars[num];
}
public static IEnumerable<string> Sort(IEnumerable<string> enumerable, string first, string second)
{
???
}
static void Main(string[] args)
{
Random rand = new Random();
string[] input = Enumerable.Range(1, 10).Select(x => GetLetter(rand) + "").ToArray();
var result = Sort(Sort(input, "c", "f"), "m", "e");
}
Supporting multiple elements ("m", "c", "f") and multiple rules is desirable if it doesn't complicate things too much.
This method does what you want:
public static IEnumerable<string> Sort(this IEnumerable<string> enumerable, string first, string second)
{
return enumerable.TakeWhile(s => s != second)
.Concat(enumerable.SkipWhile(s => s != second).OrderBy(a => a != first));
}
The idea is that first the part of the list is taken until the first f (in this case). Then the remaining part is appended to it, sorted by the c characters first.
A drawback is that the list is enumerated twice (partly). If this is performance-critical you should go for an alternative that enumerates only once.
This is a solution:
string[] ch = {"a", "c", "f", "d", "e", "c", "g", "f", "m"};
var res = ch.Select((item, index) => new { item, index })
.OrderBy(x => x.item == "c" ? 0 : Convert.ToInt32(x.index))
.Select(c => c.item).ToArray();
The output:
If In understood your question correctly I think you need to have a array rules in which you will defined the rules like which character should come first. Here I am adding a test considering your seniors. You can modify the rules and use it.
[Test]
public void CustomOrderByTests()
{
char[] ch = { 'a', 'c', 'f', 'd', 'e', 'c', 'g', 'f', 'm' };
char[] rules = { 'a', 'f', 'c' };
var result = rules.Intersect(ch).Union(ch);
char[] expected = { 'a', 'f', 'c', 'd', 'e', 'g', 'm' };
CollectionAssert.AreEqual(result, expected);
}
If you want duplicate element at same position before use Array.Sort() overload it will short the result without removing the duplicates
Array.Sort(rules, ch);
now your ch array will have sorted array.

Displaying total number of common and uncommon elements between two arrays?

I have two arrays: array testAnswer holds "answers to a exam" and array inputAnswers holds "students answers to the exam".
When i run my code, it displays all the common elements of the two arrays(correct answers), and the uncommon elements (incorrect answers). However, instead of actually displaying the correct/incorrect answers, i want to be able to display the total number of correct/incorrect answers.
My code so far:
private void button1_Click(object sender, EventArgs e)
{
//Array holding answers to test
string[] testAnswer = new string[20] { "B", "D", "A", "A", "C", "A", "B", "A", "C", "D", "B", "C", "D", "A", "D", "C", "C", "B", "D", "A" };
string a = String.Join(", ", testAnswer);
//Reads text file line by line. Stores in array, each line of the file is an element in the array
string[] inputAnswer = System.IO.File.ReadAllLines(#"C:\Users\Momo\Desktop\UNI\Software tech\test.txt");
string b = String.Join(", ", inputAnswer);
//Increments through array elements in both arrays and checks for matching elements. Displays in listBox.
for (int i = 0; i < testAnswer.Length; i++)
{
if (testAnswer[i] == inputAnswer[i])
listBox1.Items.Add(inputAnswer[i]); // or testAnswer[i], as appropriate
}
//Increments through array elements in both arrays and checks for uncommon elements. Displays in listBox.
for (int i = 0; i < testAnswer.Length; i++)
{
if (testAnswer[i] != inputAnswer[i])
listBox2.Items.Add(inputAnswer[i]);
}
}
Here's how to get your results using LINQ:
var results =
testAnswer
.Zip(inputAnswer, (t, i) => new { t, i })
.Aggregate(new { Correct = 0, Incorrect = 0 },
(a, ti) => new
{
Correct = a.Correct + (ti.t == ti.i ? 1 : 0),
Incorrect = a.Incorrect + (ti.t != ti.i ? 1 : 0)
});
It'll produce an anonymous variable with this kind of result:
An alternative approach is:
var query =
testAnswer
.Zip(inputAnswer, (t, i) => t == i)
.ToLookup(x => x);
var results = new
{
Correct = query[true].Count(),
Incorrect = query[false].Count()
};
The following code will provide 2 integers at the end which will hold the answer:
private void button1_Click(object sender, EventArgs e)
{
string[] testAnswer = new string[20] { "B", "D", "A", "A", "C", "A", "B", "A", "C", "D", "B", "C", "D", "A", "D", "C", "C", "B", "D", "A" };
string a = String.Join(", ", testAnswer);
//Reads text file line by line. Stores in array, each line of the file is an element in the array
string[] inputAnswer = System.IO.File.ReadAllLines(#"C:\Users\Momo\Desktop\UNI\Software tech\test.txt");
string b = String.Join(", ", inputAnswer);
//Increments through array elements in both arrays and checks for matching elements.
//Displays in listBox.
for (int i = 0; i < testAnswer.Length; i++)
{
if (testAnswer[i] == inputAnswer[i])
listBox1.Items.Add(inputAnswer[i]); // or testAnswer[i], as appropriate
else
listBox2.Items.Add(inputAnswer[i]);
}
int correctAns = listbox1.Items.Count;
int wringAns = listbox2.Items.Count;
}
Common answers count would be Enumerable.Intersect result item count, uncommon - Enumerable.Except result item count.
Update: as long as it was mentioned in comments that it would produce wrong answers, proof that it would not:
var testAnswers = new[] { 1, 2, 3 };
var inputAnswers = new[] { 3, 2, 1 };
var commonAnswers = testAnswers
.Select((x, index) => Tuple.Create(x, index))
.Intersect(inputAnswers.Select((y, index) => Tuple.Create(y, index)));

String Array. Select

I have the following string arrays:
var array1 = new String[] { "A", "B", "C", "D" }
var array2 = new String[] { "B", "D" }
I need to do the following:
1) Find the item in array2 which appears firts in array1 (In this case is B);
2) Get the item in (1) and all the others which appear after it in array1.
So in this case I would get:
var array3 = new String[] { "B", "C", "D" }
I was trying to do it, in one step, using a lambda expression.
Is this possible?
var array3 = array1.SkipWhile(x => !array2.Contains(x)).ToArray();

Copy one string array to another

How can I copy a string[] from another string[]?
Suppose I have string[] args. How can I copy it to another array string[] args1?
To create a completely new array with the same contents (as a shallow copy): call Array.Clone and just cast the result.
To copy a portion of a string array into another string array: call Array.Copy or Array.CopyTo
For example:
using System;
class Test
{
static void Main(string[] args)
{
// Clone the whole array
string[] args2 = (string[]) args.Clone();
// Copy the five elements with indexes 2-6
// from args into args3, stating from
// index 2 of args3.
string[] args3 = new string[5];
Array.Copy(args, 2, args3, 0, 5);
// Copy whole of args into args4, starting from
// index 2 (of args4)
string[] args4 = new string[args.Length+2];
args.CopyTo(args4, 2);
}
}
Assuming we start off with args = { "a", "b", "c", "d", "e", "f", "g", "h" } the results are:
args2 = { "a", "b", "c", "d", "e", "f", "g", "h" }
args3 = { "c", "d", "e", "f", "g" }
args4 = { null, null, "a", "b", "c", "d", "e", "f", "g", "h" }
Allocate space for the target array, that use Array.CopyTo():
targetArray = new string[sourceArray.Length];
sourceArray.CopyTo( targetArray, 0 );
The above answers show a shallow clone; so I thought I add a deep clone example using serialization; of course a deep clone can also be done by looping through the original array and copy each element into a brand new array.
private static T[] ArrayDeepCopy<T>(T[] source)
{
using (var ms = new MemoryStream())
{
var bf = new BinaryFormatter{Context = new StreamingContext(StreamingContextStates.Clone)};
bf.Serialize(ms, source);
ms.Position = 0;
return (T[]) bf.Deserialize(ms);
}
}
Testing the deep clone:
private static void ArrayDeepCloneTest()
{
//a testing array
CultureInfo[] secTestArray = { new CultureInfo("en-US", false), new CultureInfo("fr-FR") };
//deep clone
var secCloneArray = ArrayDeepCopy(secTestArray);
//print out the cloned array
Array.ForEach(secCloneArray, x => Console.WriteLine(x.DateTimeFormat.DateSeparator));
//modify the original array
secTestArray[0].DateTimeFormat.DateSeparator = "-";
Console.WriteLine();
//show the (deep) cloned array unchanged whereas a shallow clone would reflect the change...
Array.ForEach(secCloneArray, x => Console.WriteLine(x.DateTimeFormat.DateSeparator));
}

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