Linq query - find strings based upon first letter b/w two ranges

Question

We have a list containing names of countries. We need to find names of countries from list b/w two letters. Like names of all countries with name starting b/w A-G and so on. We create following linq query but its ugly.

var countryAG = from elements in countryList
where elements.StartsWith("A") || 
elements.StartsWith("B") || 
elements.StartsWith("C") || 
elements.StartsWith("D") || 
elements.StartsWith("E") || 
elements.StartsWith("F") || 
elements.StartsWith("G") || 
elements.StartsWith("H") 
select elements;

where countryList is created in C#

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

Any help or any other efficient way to accomplish above task?

Solution 1

var countryAG = from elements in countryList
                where elements[0] >= 'A' && elements[0] <= 'H'
                select elements;

Chars are just numbers really, thus you can compare them as such

Solution 2

I can't test it right now, but I would try

countryList.Where((s) => s[0] <= 'A' && s[0] >= 'G');

Solution 3

Try

char[] startingLetters = new char[] {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H'};
var countryAG = 
    from elements in countryList 
    where elements.IndexOfAny(startingLetters, 0, 1) == 0 
    select elements;

See here for information on IndexOfAny.

Solution 4

You could use a prefix list and then use the prefix list for comparison - this way you can easily use different prefix lists based on what range you are interested in:

 List<string> prefixList = new List<string>() { "A", "B", "C", "D", "E", "F", "G" };
 var countryAG = countryList.Where( x=> prefixList.Any( p => x.StartsWith(p)));

Solution 5

Try use this code:

var start = "a";
var end = "g";
var regex = new Regex(string.Format("^[{0}-{1}]", start, end));
var result = list.Where(x => regex.Match(x.ToLowerInvariant()).Success);

'start' and 'end' are static as an example.

View more solutions

Comments

[svick]

That query won't compile, you forgot select.

[Malik]

Thanks @Steven but following error during build:A query body must end with a select clause or a group clause

[Malik]

@svick, where i should add select?

[Malik]

Thanks @Broken but it is same as my current approach. I am not interested in writing all English alphabets.

[Malik]

Thanks @Yahia but it is same as my current approach. I am not interested in writing all English alphabets.

[Yahia]

sorry to read that - you asked for a more efficient way... I would bet that the query from my answer runs faster than the one you are currently using and thus I suggested it...

[Malik]

Worked like a charm. Thanks @Steven.

[Malik]

Worked like a charm. Thanks @svick for all the help.

[Malik]

Worked like a charm. Thanks @Yahia for your reply.

[Malik]

Using regex sounds interesting. I will give this a try. Thanks for your reply.

[svick]

Instead of Match().Success, you can use IsMatch().

[Malik]

Sorry @Yahia. I ignore efficiency aspect as I was constructing on "making things simple" and ignore "efficient" part. Sorry again. Also, do we have any way of "making things simple and efficient". Scenario is simple, we have list of countries name and we have to divide them among A-G, I-P and Q-Z. I thought Linq is quick and easy. Your thoughts please.

[chrisaut]

Sorry, thats what I get for writing directly inside the browser :-) Thnx svick