Checking an condition on an item in a list without foreach

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How can I check for a condition on an item in a list without using foreach. For example, instead of having to do:

C#

foreach(string[] item in mylist)
{
  if(Convert.ToBoolean(item[0]){}
}

I can just access mylist's item directly. How can I achieve this?

Thanks!

Posted 9-Nov-15 2:05am

Member 11971544

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ZurdoDev 9-Nov-15 8:13am

What specific control is it? You could likely do linq if it has a collection or list of items.

BillWoodruff 9-Nov-15 11:41am

your code: foreach(string[] item in mylist)

this implies that 'mylist contains a collection of string[]: is that correct ? if that is correct, then the Linq operator to consider here is 'SelectMany which will "flatten" a collection of collections.

Please clarify exactly what 'mylist is.

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BillWoodruff · Answer 1 · 2015-11-09T04:03:00

First, there's no way you will locate the first item in a list that matches a condition, or, all items in a List that match some condition without iteration: using Linq will just "automate" that for you.

The question for you to clarify here is what exactly you want returned from your iteration of a list of strings:

1. a list of indexes in the list where strings convertible to bool values are ?

2. or, a just a bunch of boolean values in a list: without the indexes, hard to imagine a use for that.

3. or, to take some action (execute some code) for each string that can be converted to bools based on the boolean value and/or the index of that value in the list of strings ? imho, a more plausible use-case.

4. see my comment on your post above for what else you need to clarify

I'll show you an example here of returning the list of strings as a Dictionary<int, bool> ... where the 'key is the index of the boolean value in the list, and the value is the converted boolean value.

C#

// required
using System.Linq

// assume the data source here is a simple List<string>
List<string> strList = new List<string>
{
    "True", "what", "False", "True", "ozone", "False"
};

// this variable must be initialized to be used in the Linq shown here
bool booltest = false;

Dictionary<int,bool> dctIntBool = strList
.Select((str, index) => new {index, str})
.Where(pair => Boolean.TryParse(pair.str, out booltest))
.ToDictionary(pair => pair.index, pair => booltest);

Note the variation of Linq 'Select that creates/preserves an index of the collection it iterates is used here: each pair of index/value is projected into a new anonymous structure; then, the Where Linq statement filters those "pairs" so any pair where the string is not convertible to 'bool is discarded; finally, Linq ToDictionary is used to create the Dictionary structure, using, for the Value of each KeyValuePair the boolean value assigned to 'booltest by the 'TryParse statement in the Where clause.

phil.o · Answer 2 · 2015-11-09T03:52:00

If you want to iterate over a collection, and do not want to use the foreach loop, you do not have much more choices than a for loop. This way (I assume mylist is an IList):

C#

int count = mylist.Count;
string[] result; // This assumes you have an IList<string[]>
for (int i = 0; i < count; i++)
{
   result = mylist[i];
   bool value = Convert.ToBoolean(result[0]);
}

I cannot see the reason why you are working with a list of string-arrays to get a boolean. There must be obviously a better/cleaner implementation.

Hope this helps. Good luck.

Maciej Los · Answer 3 · 2015-11-09T03:55:00

Solution 3

If you mean List<T>, you may use List.Contains method[^].

C#

List<string> mylist = new List<string>(){"cat","dog","bird"};

var result = mylist.Contains("bird");
Console.WriteLine("A list {0} 'bird' word", result==true ? "contains" : "does not contain");

Posted 9-Nov-15 3:55am

Maciej Los

Sergey Alexandrovich Kryukov · Answer 4 · 2015-11-09T04:37:00

There is no such thing as miracle. If you use some method without a loop, it means that some loop is used behind the hood. But it often make perfect sense to use such methods. See, in particular, generic method System.Array.ForEach<>:
https://msdn.microsoft.com/en-us/library/zecdkyw2%28v=vs.110%29.aspx[^].

—SA

Krunal Rohit · Answer 5 · 2015-11-09T02:17:00

Solution 1

I don't know what you're trying to do but look at this -

C#

var check = Convert.ToBoolean(mylist.First()); // this will give you the First element of the array
if(check)
{
    // do something
}

-KR

Posted 9-Nov-15 2:17am

Krunal Rohit

Comments

Member 11971544 9-Nov-15 8:21am

In case I want to get the second, third, fourth.. elements?

Krunal Rohit 9-Nov-15 8:23am

Meaning you want the item based on some condition ?

-KR

Member 11971544 9-Nov-15 8:25am

yes, so if(second element in the list is true as well) //do something

Krunal Rohit 9-Nov-15 8:26am

See, that you can do using loop. But if you want to get only items which is true, you can get it with LINQ.
So, elaborate your issue what you're trying to do ?

-KR

Member 11971544 9-Nov-15 8:41am

So I have a List<string[]> and I'm trying to check if each item in the list is true but avoiding using a foreach/for loop as it wouldn't go in with the logic of my method. How can I achieve it with LINQ?

Krunal Rohit 9-Nov-15 8:47am

If you want to perform something within the condition, you have to use loops.
LINQ will give you items which are true, but still you have to loop through the true items.

-KR

Member 11971544 9-Nov-15 8:55am

Alright got it, thank you.

Roger C Moore · Answer 6 · 2024-03-08T07:37:00

Solution 6

You could use a lambda function, which are like improve anonymous methods, that makes the condition easier to read:

bool exists = myList.Any(x => Convert.ToBoolean(x) == true);
if (exists) {
    // Do something
}

Posted 8-Mar-24 7:37am

Roger C Moore

Updated 8-Mar-24 7:39am

v3

Comments

Graeme_Grant 8-Mar-24 18:27pm

This is an 8 year old question. Please focus on current questions only.

Richard Deeming 18-Mar-24 10:03am

The age of the question isn't relevant - IF the answer adds something new to the discussion.

As far as I can see, none of the previous answers mentioned using LINQ's Any method, so that's something in its favour.

However, the supplied code will not work for the OP, who is dealing with a list of string arrays. Convert.ToBoolean is going to throw an exception as soon as it hits the first item!

There's also no point in the == true part; Convert.ToBoolean already returns a bool.

Checking an condition on an item in a list without foreach

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