Find index of a value in an array

Question

Can linq somehow be used to find the index of a value in an array   For instance  this loop locates the key index within an array   for  int i   0  i  lt  words Length  i          if  words i  IsKey                keyIndex   i

User · Answer

If you want to find the word you can use

var word = words.Where(item => item.IsKey).First();

This gives you the first item for which IsKey is true (if there might be non you might want to use .FirstOrDefault()

To get both the item and the index you can use

KeyValuePair<WordType, int> word = words.Select((item, index) => new KeyValuePair<WordType, int>(item, index)).Where(item => item.Key.IsKey).First();

User · Answer

This solution helped me more  from msdn microsoft   var result    query AsEnumerable   Select  x  index    gt                new   index x Id x FirstName      query is your toList   query

User · Answer

int keyIndex   Array FindIndex words  w   gt  w IsKey     That actually gets you the integer index and not the object  regardless of what custom class you have created

User · Answer

Try this     var key   words Where x   gt  x IsKey    true

User · Answer

Just posted my implementation of IndexWhere   extension method  with unit tests    http   snipplr com view 53625 linq-index-of-item--indexwhere   Example usage   int index   myList IndexWhere item   gt  item Something    someOtherThing

User · Answer

For arrays you can use  Array FindIndex lt T gt    int keyIndex   Array FindIndex words  w   gt  w IsKey       For lists you can use List lt T gt  FindIndex   int keyIndex   words FindIndex w   gt  w IsKey       You can also write a generic extension method that works for any Enumerable lt T gt        lt summary gt Finds the index of the first item matching an expression in an enumerable  lt  summary gt      lt param name  items  gt The enumerable to search  lt  param gt      lt param name  predicate  gt The expression to test the items against  lt  param gt      lt returns gt The index of the first matching item  or -1 if no items match  lt  returns gt  public static int FindIndex lt T gt  this IEnumerable lt T gt  items  Func lt T  bool gt  predicate        if  items    null  throw new ArgumentNullException  items        if  predicate    null  throw new ArgumentNullException  predicate         int retVal   0      foreach  var item in items            if  predicate item   return retVal          retVal              return -1        And you can use LINQ as well   int keyIndex   words      Select  v  i    gt  new  Word   v  Index   i        FirstOrDefault x   gt  x Word IsKey   Index    -1

User · Answer

int keyIndex   words TakeWhile w   gt   w IsKey  Count

User · Answer

int index   -1  index   words Any  word   gt    index    return word IsKey       index   -1

[c#] Find index of a value in an array

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