How do I select words that contain certain letter at certain positions using C# LINQ lambda expressions

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lets say I have array of strings:

string[] digits = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "specific"};

How can I select only words that contain i at position 2 (index 1).
So that output is only: five, six, eight and nine?

What I have tried:

string[] digits = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "specific"};

            var res = digits.Where(w => "i".All(l => w.Contains(l)))
//I know this is incorrect... just provided my try

return res;

Posted 1-Mar-22 5:55am

LuckyChloe

Updated 1-Mar-22 6:25am

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2 solutions

Solution 2

You can also use Regex[^]. See:

string[] digits = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "specific"};

string pattern = @"^\w{1}i";
Regex r = new Regex(pattern);

var result = digits.Where(word => r.IsMatch(word)).ToList();

^\w{1}i pattern means:
^ - asserts position at start of a line
\w{1} - matches any word character (equivalent to [a-zA-Z0-9_]), exactly one occurence
i - find exact match, a letter i

More at: regex101: build, test, and debug regex[^]

Posted 1-Mar-22 6:25am

Maciej Los

Comments

LuckyChloe 1-Mar-22 13:52pm

We have not covered Regex yet but once we do will take a look at it ❤️
trying to learn LINQ first.

Maciej Los 1-Mar-22 15:05pm

As you can see, i use Linq query and inside it - a regex method :D

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Luc Pattyn · Accepted Answer · 2022-03-01T05:59:00

Solution 1

How would you do it without LINQ? With LINQ it is the same:

C#

var res = digits.Where(w => w[1]=='i')

Posted 1-Mar-22 5:59am

Luc Pattyn

Comments

LuckyChloe 1-Mar-22 12:05pm

Thank you!.
Without LINQ I was thinking it was possible to do it using if statements

Luc Pattyn 1-Mar-22 12:08pm

The Where() method IS just an if statement!
Where(someCondition) is equivalent to

foreach(item in IEnumerable) {
    if (!someCondition) continue;
    /// proceed with this item
}

LuckyChloe 1-Mar-22 12:09pm

I did not know that. I realized that they were similar but no in that way. Thank you.

OriginalGriff 1-Mar-22 12:29pm

Be aware that what Luc says is an oversimplification - Linq methods aren't really the same as an "explicit loop" - they use something called "deferred execution" where the code isn't executed at all until you actually need it - and that can cause some real confusion if you aren't careful.
An IEnumerable (which is what the Where call will return) is not the same as a List!

Luc Pattyn 1-Mar-22 12:48pm

I don't like overcomplicating things.
If you read "/// proceed with this item" as "yield return item" you're pretty close to what is really going on, the foreach code is being generated by the compiler and the whole thing IS an IEnumerable.
But I'm afraid that is too much information for a first LINQ encounter.