Most efficient method to create all the letters in the alphabet into a string

Question

Possible Duplicate:
Generating an array of letters in the alphabet in C#

(Theoretical question only, was just pondering it as a writing a filtering system (not using an alphabet, but got me thinking)).

So lets say I want to create a filter list of all the capital letters (A-Z) in the English alphabet plus the word "All"

All A B C D E ... X Y Z

And convert it to a List<string> what is the most efficient way to do this in C# Without using the hard coded {"A","B"} method.

Not a duplicate of This question

The question listed above deals with conversion to a plain and simple character array, which wouldn't allow for the ALL portion. And to take that and convert I believe would involve at least a copy + cast.

@NikolaAnusev not a duplicate I'm afraid, the other one uses a CharArray which wouldn't support the All section, and using this method would require a copy + append. — John Mitchell, Jul 29 '12 at 20:47
You are probably right - it's not an *exact* duplicate, but I don't think answers here will be much different. — Nikola Anusev, Jul 29 '12 at 20:57
Why do you want to create a list of strings for a list of chars? — Tim Schmelter, Jul 29 '12 at 20:59
@TimSchmelter because of the first requirement (adding the word "All" to the list) — John Mitchell, Jul 29 '12 at 22:50
It's worth mentioning that hard coding it would be the most efficient. If you can't about efficiency to that, if you don't, then so whatever you feel like regardless of efficiency. — Servy, Jul 29 '12 at 22:52

score 2 · Answer 1 · answered Jul 29 '12 at 20:56

2

You can also do it with actual characters:

List<string> characters = new List<string>();

for (char c = 'A'; c <= 'Z'; c++)
    characters.Add("" + c);

answered Jul 29 '12 at 20:56

Balázs Édes

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Or change the first line to `var characters = new List(27) { "All", };`. Then the capacity of the `List<>` will not need to be expanded during the loop. – Jeppe Stig Nielsen Jul 29 '12 at 21:32

score 2 · Accepted Answer · answered Jul 29 '12 at 22:35

For 'most efficient' you would try to avoid List<> and LINQ.

  var sb = new StringBuilder("All", 26+3 +spare);
  for (char c = 'A'; c <= 'Z'; c++)  sb.Append(c);

  string result = sb.ToString();

but to be honest you would have to benchmark the various answers here.

score 1 · Answer 3 · answered Jul 29 '12 at 20:48

1

Each string character is a char value that has a number an ascii. Capital A starts at 65 and Captial Z is 90. Thus using a loop you can generate the values.

List<string> alpha = new List<string>();
for(int i=65; i <=90; i++) {
   alpha.add(""+(char)i);
}

EDIT:

You could also use the character literals for the for loop as

for(int i = (int)'A'; i <= (int)'Z'; i++)

answered Jul 29 '12 at 20:48

secretformula

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2

`for(int i = (int)'A'; i <= (int)'Z'; i++)` would be better. – Zong Jul 29 '12 at 20:49
2

Why not just `for (char c = 'A'; c <= 'Z'; c++) alpha.Add(c.ToString());`? – Jeppe Stig Nielsen Jul 29 '12 at 21:27

Tim Schmelter · Answer 4 · 2012-07-29T21:46:09.330

For example:

var alphabet = new List<String>(27);
var capitalRange = Enumerable.Range(0, 26)
    .Select(i => new String(Convert.ToChar(i + 65), 1));
alphabet.AddRange( capitalRange );
alphabet.Add("All");

Note that the initialization of the list with the correct capacity ensures that it doesn't need to be resized and won't be oversized. Apart from that this is similar to a for-loop. The string constuctor is slightly faster than a Char.ToString().

score 0 · Answer 5 · answered Jul 29 '12 at 21:36

Here is a fairly compact way to do it:

var list = new[] { "All" }.Concat(
    Enumerable.Range('A', 'Z' - 'A' + 1)
    .Select(c => ((char)c).ToString())
).ToList();

But something like this is cleaner (IMO) and more efficient since there is no resizing:

const char start_ch = 'A';
const char end_ch = 'Z';

var list = new List<string>(end_ch - start_ch + 1) { "All" };

for (char ch = start_ch; ch <= end_ch; ++ch)
    list.Add(ch.ToString());

What exactly do you intend to do with this List? For example, searching can be more efficiently done using an associative data structure instead, such as HashSet or Dictionary.

Nothing :) it was a theoretical question about micro-optomization thats all. If it was just output then I'd probably use a array, if it was searching then it'd be a dictionary. — John Mitchell, Jul 29 '12 at 21:53

Most efficient method to create all the letters in the alphabet into a string

5 Answers5