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Check if list contains element that contains a string and get that element

Posted by: admin November 30, 2017 Leave a comment

Questions:

While searching for an answer to this question, I’ve run into similar ones utilizing LINQ but I haven’t been able to fully understand them (and thus, implement them), as I’m not familiarized with it. What I would like to, basically, is this:

  1. Check if any element of a list contains a specific string.
  2. If it does, get that element.

I honestly don’t know how I would go about doing that. What I can come up with is this (not working, of course):

if (myList.Contains(myString))
    string element = myList.ElementAt(myList.IndexOf(myString));

I know WHY it does not work:

  • myList.Contains() does not return true, since it will check for if a whole element of the list matches the string I specified.
  • myList.IndexOf() will not find an occurrence, since, as it is the case again, it will check for an element matching the string.

Still, I have no clue how to solve this problem, but I figure I’ll have to use LINQ as suggested in similar questions to mine. That being said, if that’s the case here, I’d like for the answerer to explain to me the use of LINQ in their example (as I said, I haven’t bothered with it in my time with C#). Thank you in advance guys (and gals?).

EDIT: I have come up with a solution; just loop through the list, check if current element contains the string and then set a string equal to the current element. I’m wondering, though, is there a more efficient way than this?

string myString = "bla";
string element = "";

for (int i = 0; i < myList.Count; i++)
{
    if (myList[i].Contains(myString))
        element = myList[i];
}
Answers:

You should be able to use Linq here:

var matchingvalues = myList
    .Where(stringToCheck => stringToCheck.Contains(myString));

If you simply wish to return the first matching item:

var match = myList
    .FirstOrDefault(stringToCheck => stringToCheck.Contains(myString));

if(match != null)
    //Do stuff

Questions:
Answers:

The basic answer is
You need to iterate through loop and check any element contains the specified string.
So, Lets say code is

foreach(string item in myList)
{
  if(item.Contains(myString))
       return item;
}

The equivalent but terse code is

mylist.Where(x => x.Contains(myString)).FirstOrDefault();

Here,
x is parameter that acts like item in above code.

Questions:
Answers:
string result = myList.FirstOrDefault(x => x == myString)
if(result != null)
{
  //found
}

Questions:
Answers:
for (int i = 0; i < myList.Length; i++)
{
    if (myList[i].Contains(myString)) // (you use the word "contains". either equals or indexof might be appropriate)
    {
        return i;
    }
}

Old fashion loops are almost always the fastest.

Questions:
Answers:

If you want a list of strings containing your string:

var newList = myList.Where(x => x.Contains(myString)).ToList();

Another option is to use Linq FirstOrDefault

var element = myList.Where(x => x.Contains(myString)).FirstOrDefault();

Keep in mind that Contains method is case sensitive.

Questions:
Answers:

You could use Linq’s FirstOrDefault extension method:

string element = myList.FirstOrDefault(s => s.Contains(myString));

This will return the fist element that contains the substring myString, or null if no such element is found.

If all you need is the index, use the List<T> class’s FindIndex method:

int index = myList.FindIndex(s => s.Contains(myString));

This will return the the index of fist element that contains the substring myString, or -1 if no such element is found.

Questions:
Answers:

you can use

var match=myList.Where(item=>item.Contains("Required String"));
foreach(var i in match)
{
//do something with the matched items
}

LINQ provides you with capabilities to “query” any collection of data. You can use syntax like a database query (select, where, etc) on a collection (here the collection (list) of strings).

so you are doing like “get me items from the list Where it satisfies a given condition”

inside the Where you are using a “lambda expression”

to tell briefly lambda expression is something like (input parameter => return value)

so for a parameter “item”, it returns “item.Contains(“required string”)” . So it returns true if the item contains the string and thereby it gets selected from the list since it satisfied the condition.

Questions:
Answers:

To keep it simple use this;

foreach(string item in myList)//Iterate through each item.
{
 if(item.Contains("Search Term")//True if the item contains search pattern.
 {
   return item;//Return the matched item.
 }
}

Alternatively,to do this with for loop,use this;

    for (int iterator = 0; iterator < myList.Count; iterator++)
    {
        if (myList[iterator].Contains("String Pattern"))
        {
            return myList[iterator];
        }
    }