Develop Reference

Need to refer to second to the last element of array of partial filenames

I need to find distinct values of partial filenames in an array of filenames. I'd like to do it in one line.
So, I have something like that as a filenames:
string[] filenames = {"aaa_ab12345.txt", "bbb_ab12345.txt", "aaa_ac12345.txt", "bbb_ac12345"}
and I need to find distinct values for ab12345 part of it.
So I currently have something like that:
string[] filenames_partial_distinct = Array.ConvertAll(
filenames,
file => System.IO.Path.GetFileNameWithoutExtension(file)
.Split({"_","."}, StringSplitOptions.RemoveEmptyEntries)[1]
)
.Distinct()
.ToArray();
Now, I'm getting filenames that are of form of aaa_bbb_ab12345.txt. So, instead of referring to the second part of the filename, I need to refer to the second to the last.
So, how do I refer to an arbitrary element based on length of array in one line, if it's a result of Split method? Something along lines of:
Array.ConvertAll(filenames, file=>file.Split(separator)[this.Length-2]).Distinct().ToArray();
In other words, if a string method results in an array of strings, how do I immediately select element based on the length of array:
String.Split()[third from end, fifth from end, etc.];

If you use GetFileNameWithoutExtension there will be no extension and therefore splitting by '_' will do it. Then you can take the last part with .Last().
string[] filenames_partial_distinct = Array.ConvertAll(
filenames,
file => Path.GetFileNameWithoutExtension(file).Split('_').Last()
)
.Distinct()
.ToArray();
With the input
string[] filenames = { "aaa_ab12345.txt", "bbb_ab12345.txt",
"aaa_ac12345.txt", "bbb_ac12345", "aaa_bbb_ab12345.txt" };
You get the result
{ "ab12345", "ac12345" }
The StringSplitOptions.RemoveEmptyEntries is only required if there are filenames ending with _ (before the extension).

Seems you're looking for something like this:
string[] arr = filenames.Select(n => n.Substring(n.IndexOf("_") + 1, 7)).Distinct().ToArray();

I usually defer problems like this to regex. They are very powerful. This approach also gives you the opportunity to detect unexpected cases and handle them appropriately.
Here is a crude example, assuming I understood your requirements:
using System;
using System.Linq;
using System.Text.RegularExpressions;
public class Program
{
public static void Main()
{
string MyMatcher(string filename)
{
// this pattern may need work depending on what you need - it says
// extract that pattern between the "()" which is 2 characters and
// 4 digits, exactly; and can be found in `Groups[1]`.
Regex r = new Regex(#".*_(\w{2}\d{4}).*", RegexOptions.IgnoreCase);
Match m = r.Match(filename);
return m.Success
? m.Groups[1].ToString()
: null; // what should happen here?
}
string[] filenames =
{
"aaa_ab12345.txt",
"bbb_ab12345.txt",
"aaa_ac12345.txt",
"bbb_ac12345",
"aaa_bbb_ab12345.txt",
"ae12345.txt" // MyMatcher() return null for this - what should you do if this happens?
};
var results = filenames
.Select(MyMatcher)
.Distinct();
foreach (var result in results)
{
Console.WriteLine(result);
}
}
}
Gives:
ab1234
ac1234
This can be refined further, such as pre-compiled regex patterns, encapsulation in a class, etc.

Equals() method not recognizing similar/same characters when comparing

Why comparing characters with .Equals always returns false?
char letter = 'a';
Console.WriteLine(letter.Equals("a")); // false
Overall I'm trying to write an English - Morse Code translator. I run into a problem comparing char values which shown above. I began with a foreach to analyze all the characters from a ReadLine() input, by using the WriteLine() method, all the characters were transposed fine, but when trying to compare them using the .Equals() method, no matter what I did, it always output false when trying to compare chars.
I have used the .Equals() method with other strings successfully, but it seems to not work with my chars.
using System;
public class MorseCode {
public static void Main (string[] args) {
Console.WriteLine ("Hello, write anything to convert it to morse code!");
var input = Console.ReadLine();
foreach (char letter in input) {
if(letter.Equals("a")) {
Console.WriteLine("Its A - live");
}
Console.WriteLine(letter);
}
var morseTranslation = "";
foreach (char letter in input) {
if(letter.Equals("a")) {
morseTranslation += ". _ - ";
}
if(letter.Equals("b")) {
morseTranslation += "_ . . . - ";
}
if(letter.Equals("c")) {
morseTranslation += "_ . _ . - ";
}
...
}
}
Console.WriteLine("In morse code, " + input + " is '"morseTranslation + "'");
}
}
At the beginning, I wrote the foreach to test if it recognized and ran the correct output, but in the end, when I wrote "sample" into the ReadLine(), it gave me :
Hello, write anything to convert it to morse code!
sample
s
a
m
p
l
e

When you do this:
var c = 'x';
var isEqual = c.Equals("x");
the result (isEqual) will always be false because it's comparing a string to a char. This would return true:
var isEqual = c.Equals('x');
The difference is that "x" is a string literal and 'x' is a char literal.
Part of what makes this confusing is that when you use an object's Equals method, it allows you to compare any type to any other type. So you could do this:
var x = 0;
var y = "y";
var isEqual = x.Equals(y);
...and the compiler will allow it, even though the comparison between int and string won't work. It will give you this warning:
When comparing value types like int or char with other values of the same type, we usually use ==, like
if (someChar == someOtherChar)
Then if you tried to do this:
if(someChar == "a")
It wouldn't compile. It would tell you that you're comparing a char to a string, and then it's easier because instead of running the program and looking for the error it just won't compile at all and it will tell you exactly where the problem is.
Just for the fun of it, here's another implementation.
public static class MorseCodeConverter
{
private static readonly Dictionary<char, string> Codes
= CreateMorseCodeDictionary();
public static string Convert(string input)
{
var lowerCase = input.ToLower();
var result = new StringBuilder();
foreach (var character in input)
{
if (Codes.ContainsKey(character))
result.Append(Codes[character]);
}
return result.ToString();
}
static Dictionary<char, string> CreateMorseCodeDictionary()
{
var result = new Dictionary<char, string>();
result.Add('a', ". _ - ");
result.Add('b', "_ . . . - ");
// add all the rest
return result;
}
}
One difference is that it's a class by itself without the console app. Then you can use it in a console app. Read the input from the keyboard and then call
MorseCodeConverter.Convert(input);
to get the result, and then you can print it to the console.a
Putting all of the characters in a dictionary means that instead of repeating the if/then you can just check to see if each character is in the dictionary.

It's important to remember that whilst the char and string keywords look reminiscant of eachother when looking at printed values you should note that they are not accomodated for in exactly the same way.
When you check a string you can use:
string s = "A";
if(s.Equals("A"))
{
//Do Something
}
However, the above will not work with a char. The difference between chars (value types) and strings (reference types) on a surface level is the use of access - single quote (apostrophe) vs quote.
To compare a char you can do this:
char s = 'A';
if(s.Equals('A'))
{
//Do Something
}
On a point relevant to your specific case however, morse code will only requre you to use a single case alphabet and as such when you try to compare against 'A' and 'a' you can call input.ToLower() to reduce your var (string) to all lower case so you don't need to cater for both upper and lower case alphabets.
It's good that you're aware of string comparissons and are not using direct value comparisson as this:
if (letter == 'a')
{
Console.WriteLine("Its A - live");
}
Would've allowed you to compare the char but it's bad practice as it may lead to lazy comparisson of strings in the same way and this:
if (letter == "a")
{
Console.WriteLine("Its A - live");
}
Is a non-representitive method of comparison for the purpose of comparing strings as it evaluates the reference not the direct value, see here

For char comparison you have to use single quote ' character not " this.
By the way it writes sample in decending order beacuse in your first foreach loop you write all letters in new line. SO below code will work for you:
using System;
public class MorseCode {
public static void Main (string[] args) {
Console.WriteLine ("Hello, write anything to convert it to morse code!");
var input = Console.ReadLine();
/*foreach (char letter in input) {
if(letter.Equals("a")) {
Console.WriteLine("Its A - live");
}
Console.WriteLine(letter);
}*/
var morseTranslation = "";
foreach (char letter in input) {
if(letter.Equals('a')) {
morseTranslation += ". _ - ";
}
if(letter.Equals('b')) {
morseTranslation += "_ . . . - ";
}
if(letter.Equals('c')) {
morseTranslation += "_ . _ . - ";
}
...
}
}
Console.WriteLine("In morse code, " + input + " is '"morseTranslation + "'");
}
}

In C#, you can compare strings like integers, that is with == operator. Equals is a method inherited from the object class, and normally implementations would make some type checks. char letter is (obviously) a character, while "a" is a single lettered string.
That's why it returns false.
You could use if (letter.Equals('a')) { ... }, or simpler if (letter == 'a') { ... }
Even simpler than that would be switch (letter) { case 'a': ...; break; ... }.
Or something that is more elegant but maybe too advanced yet for a beginner, using LINQ:
var validCharacters = "ABCDE...";
var codes = new string[] {
".-", "-...", "-.-.", "-..", ".", ...
};
var codes = input.ToUpper() // make uppercase
.ToCharArray() // explode string into single characters
.Select(validCharaters.IndexOf) // foreach element (i. e. character), get the result of "validCharacters.IndexOf",
// which equals the index of the morse code in the array "codes"
.Where(i => i > -1) // only take the indexes of characters that were found in "validCharacters"
.Select(i => codes[i]); // retrieve the matching entry from "codes" by index
// "codes" is now an IEnumerable<string>, a structure saying
// "I am a list of strings over which you can iterate,
// and I know how to generate the elements as you request them."
// Now concatenate all single codes to one long result string
var result = string.Join(" ", codes);

Finding longest word in string

Ok, so I know that questions LIKE this have been asked a lot on here, but I can't seem to make solutions work.
I am trying to take a string from a file and find the longest word in that string.
Simples.
I think the issue is down to whether I am calling my methods on a string[] or char[], currently stringOfWords returns a char[].
I am trying to then order by descending length and get the first value but am getting an ArgumentNullException on the OrderByDescending method.
Any input much appreciated.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
namespace TextExercises
{
class Program
{
static void Main(string[] args)
{
var fileText = File.ReadAllText(#"C:\Users\RichardsPC\Documents\TestText.txt");
var stringOfWords = fileText.ToArray();
Console.WriteLine("Text in file: " + fileText);
Console.WriteLine("Words in text: " + fileText.Split(' ').Length);
// This is where I am trying to solve the problem
var finalValue = stringOfWords.OrderByDescending(n => n.length).First();
Console.WriteLine("Largest word is: " + finalValue);
}
}
}

Don't split the string, use a Regex
If you care about performance you don't want to split the string. The reason in order to do the split method will have to traverse the entire string, create new strings for the items it finds to split and put them into an array, computational cost of more than N, then doing an order by you do another (at least) O(nLog(n)) steps.
You can use a Regex for this, which will be more efficient, because it will only iterate over the string once
var regex = new Regex(#"(\w+)\s",RegexOptions.Compiled);
var match = regex.Match(fileText);
var currentLargestString = "";
while(match.Success)
{
if(match.Groups[1].Value.Length>currentLargestString.Length)
{
currentLargestString = match.Groups[1].Value;
}
match = match.NextMatch();
}
The nice thing about this is that you don't need to break the string up all at once to do the analysis and if you need to load the file incrementally is a fairly easy change to just persist the word in an object and call it against multiple strings
If you're set on using an Array don't order by just iterate over
You don't need to do an order by your just looking for the largest item, computational complexity of order by is in most cases O(nLog(n)), iterating over the list has a complexity of O(n)
var largest = "";
foreach(var item in strArr)
{
if(item.Length>largest.Length)
largest = item;
}

Method ToArray() in this case returns char[] which is an array of individual characters. But instead you need an array of individual words. You can get it like this:
string[] stringOfWords = fileText.Split(' ');
And you have a typo in your lambda expression (uppercase L):
n => n.Length

Try this:
var fileText = File.ReadAllText(#"C:\Users\RichardsPC\Documents\TestText.txt");
var words = fileText.Split(' ')
var finalValue = fileText.OrderByDescending(n=> n.Length).First();
Console.WriteLine("Longest word: " + finalValue");

As suggested in the other answer, you need to split your string.
string[] stringOfWords = fileText.split(new Char [] {',' , ' ' });
//all is well, now let's loop over it and see which is the biggest
int biggest = 0;
int biggestIndex = 0;
for(int i=0; i<stringOfWords.length; i++) {
if(biggest < stringOfWords[i].length) {
biggest = stringOfWords[i].length;
biggestIndex = i;
}
}
return stringOfWords[i];
What we're doing here is splitting the string based on whitespace (' '), or commas- you can add an unlimited number of delimiters there - each word, then, gets its own space in the array.
From there, we're iterating over the array. If we encounter a word that's longer than the current longest word, we update it.

Check for special characters (/*-+_#&$#%) in a string?

How do I check a string to make sure it contains numbers, letters, or space only?

In C# this is simple:
private bool HasSpecialChars(string yourString)
{
return yourString.Any(ch => ! char.IsLetterOrDigit(ch));
}

The easiest way it to use a regular expression:
Regular Expression for alphanumeric and underscores
Using regular expressions in .net:
http://www.regular-expressions.info/dotnet.html
MSDN Regular Expression
Regex.IsMatch
var regexItem = new Regex("^[a-zA-Z0-9 ]*$");
if(regexItem.IsMatch(YOUR_STRING)){..}

string s = #"$KUH% I*$)OFNlkfn$";
var withoutSpecial = new string(s.Where(c => Char.IsLetterOrDigit(c)
|| Char.IsWhiteSpace(c)).ToArray());
if (s != withoutSpecial)
{
Console.WriteLine("String contains special chars");
}

Try this way.
public static bool hasSpecialChar(string input)
{
string specialChar = #"\|!#$%&/()=?»«#£§€{}.-;'<>_,";
foreach (var item in specialChar)
{
if (input.Contains(item)) return true;
}
return false;
}

String test_string = "tesintg#$234524##";
if (System.Text.RegularExpressions.Regex.IsMatch(test_string, "^[a-zA-Z0-9\x20]+$"))
{
// Good-to-go
}
An example can be found here: http://ideone.com/B1HxA

If the list of acceptable characters is pretty small, you can use a regular expression like this:
Regex.IsMatch(items, "[a-z0-9 ]+", RegexOptions.IgnoreCase);
The regular expression used here looks for any character from a-z and 0-9 including a space (what's inside the square brackets []), that there is one or more of these characters (the + sign--you can use a * for 0 or more). The final option tells the regex parser to ignore case.
This will fail on anything that is not a letter, number, or space. To add more characters to the blessed list, add it inside the square brackets.

Use the regular Expression below in to validate a string to make sure it contains numbers, letters, or space only:
[a-zA-Z0-9 ]

You could do it with a bool. I've been learning recently and found I could do it this way. In this example, I'm checking a user's input to the console:
using System;
using System.Linq;
namespace CheckStringContent
{
class Program
{
static void Main(string[] args)
{
//Get a password to check
Console.WriteLine("Please input a Password: ");
string userPassword = Console.ReadLine();
//Check the string
bool symbolCheck = userPassword.Any(p => !char.IsLetterOrDigit(p));
//Write results to console
Console.WriteLine($"Symbols are present: {symbolCheck}");
}
}
}
This returns 'True' if special chars (symbolCheck) are present in the string, and 'False' if not present.

A great way using C# and Linq here:
public static bool HasSpecialCharacter(this string s)
{
foreach (var c in s)
{
if(!char.IsLetterOrDigit(c))
{
return true;
}
}
return false;
}
And access it like this:
myString.HasSpecialCharacter();

private bool isMatch(string strValue,string specialChars)
{
return specialChars.Where(x => strValue.Contains(x)).Any();
}

Create a method and call it hasSpecialChar with one parameter
and use foreach to check every single character in the textbox, add as many characters as you want in the array, in my case i just used ) and ( to prevent sql injection .
public void hasSpecialChar(string input)
{
char[] specialChar = {'(',')'};
foreach (char item in specialChar)
{
if (input.Contains(item)) MessageBox.Show("it contains");
}
}
in your button click evenement or you click btn double time like that :
private void button1_Click(object sender, EventArgs e)
{
hasSpecialChar(textbox1.Text);
}

While there are many ways to skin this cat, I prefer to wrap such code into reusable extension methods that make it trivial to do going forward. When using extension methods, you can also avoid RegEx as it is slower than a direct character check. I like using the extensions in the Extensions.cs NuGet package. It makes this check as simple as:
Add the [https://www.nuget.org/packages/Extensions.cs][1] package to your project.
Add "using Extensions;" to the top of your code.
"smith23#".IsAlphaNumeric() will return False whereas "smith23".IsAlphaNumeric() will return True. By default the .IsAlphaNumeric() method ignores spaces, but it can also be overridden such that "smith 23".IsAlphaNumeric(false) will return False since the space is not considered part of the alphabet.
Every other check in the rest of the code is simply MyString.IsAlphaNumeric().

Based on #prmph's answer, it can be even more simplified (omitting the variable, using overload resolution):
yourString.Any(char.IsLetterOrDigit);

No special characters or empty string except hyphen
^[a-zA-Z0-9-]+$

C# Regex Split To Java Pattern split

I have to port some C# code to Java and I am having some trouble converting a string splitting command.
While the actual regex is still correct, when splitting in C# the regex tokens are part of the resulting string[], but in Java the regex tokens are removed.
What is the easiest way to keep the split-on tokens?
Here is an example of C# code that works the way I want it:
using System;
using System.Text.RegularExpressions;
class Program
{
static void Main()
{
String[] values = Regex.Split("5+10", #"([\+\-\*\(\)\^\\/])");
foreach (String value in values)
Console.WriteLine(value);
}
}
Produces:
5
+
10

I don't know how C# does it, but to accomplish it in Java, you'll have to approximate it. Look at how this code does it:
public String[] split(String text) {
if (text == null) {
text = "";
}
int last_match = 0;
LinkedList<String> splitted = new LinkedList<String>();
Matcher m = this.pattern.matcher(text);
// Iterate trough each match
while (m.find()) {
// Text since last match
splitted.add(text.substring(last_match,m.start()));
// The delimiter itself
if (this.keep_delimiters) {
splitted.add(m.group());
}
last_match = m.end();
}
// Trailing text
splitted.add(text.substring(last_match));
return splitted.toArray(new String[splitted.size()]);
}

This is because you are capturing the split token. C# takes this as a hint that you wish to retain the token itself as a member of the resulting array. Java does not support this.