if statements matching multiple values

Question

Any easier way to write this if statement   if  value  1    value  2   For example    in SQL you can say where value in  1 2  instead of where value 1 or value 2   I m looking for something that would work with any basic type    string  int  etc

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Easier is subjective  but maybe the switch statement would be easier  You don t have to repeat the variable  so more values can fit on the line  and a line with many comparisons is more legible than the counterpart using the if statement

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If you have a List  you can use  Contains yourObject   if you re just looking for it existing  like a where   Otherwise look at Linq  Any   extension method

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Generally  no   Yes  there are cases where the list is in an Array or List  but that s not the general case

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Alternatively  and this would give you more flexibility if testing for values other than 1 or 2 in future  is to use a switch statement  switch value    case 1  case 2     return true  default     return false

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An extensionmethod like this would do it     public static bool In lt T gt  this T item  params T   items        return items Contains item       Use it like this   Console WriteLine 1 In 1 2 3    Console WriteLine  a  In  a    b

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In vb net or C  I would expect that the fastest general approach to compare a variable against any reasonable number of separately-named objects  as opposed to e g  all the things in a collection  will be to simply compare each object against the comparand much as you have done   It is certainly possible to create an instance of a collection and see if it contains the object  and doing so may be more expressive than comparing the object against all items individually  but unless one uses a construct which the compiler can explicitly recognize  such code will almost certainly be much slower than simply doing the individual comparisons   I wouldn t worry about speed if the code will by its nature run at most a few hundred times per second  but I d be wary of the code being repurposed to something that s run much more often than originally intended   An alternative approach  if a variable is something like an enumeration type  is to choose power-of-two enumeration values to permit the use of bitmasks   If the enumeration type has 32 or fewer valid values  e g  starting Harry 1  Ron 2  Hermione 4  Ginny 8  Neville 16  one could store them in an integer and check for multiple bits at once in a single operation   if   thisOne  amp   Harry   Ron   Neville   Beatrix      0     Do something      This will allow for fast code  but is limited to enumerations with a small number of values   A somewhat more powerful approach  but one which must be used with care  is to use some bits of the value to indicate attributes of something  while other bits identify the item   For example  bit 30 could indicate that a character is male  bit 29 could indicate friend-of-Harry  etc  while the lower bits distinguish between characters   This approach would allow for adding characters who may or may not be friend-of-Harry  without requiring the code that checks for friend-of-Harry to change   One caveat with doing this is that one must distinguish between enumeration constants that are used to SET an enumeration value  and those used to TEST it   For example  to set a variable to indicate Harry  one might want to set it to 0x60000001  but to see if a variable IS Harry  one should bit-test it with 0x00000001   One more approach  which may be useful if the total number of possible values is moderate  e g  16-16 000 or so  is to have an array of flags associated with each value   One could then code something like  if    characterAttributes theCharacter   amp  chracterAttribute Male     0     This approach will work best when the number of characters is fairly small   If array is too large  cache misses may slow down the code to the point that testing against a small number of characters individually would be faster

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public static bool EqualsAny lt T gt  IEquatable lt T gt  value  params T   possibleMatches        foreach  T t in possibleMatches            if  value Equals t               return true            return false    public static bool EqualsAny lt T gt  IEquatable lt T gt  value  IEnumerable lt T gt  possibleMatches        foreach  T t in possibleMatches            if  value Equals t               return true            return false

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If you search a value in a fixed list of values many times in a long list  HashSet lt T gt  should be used  If the list is very short   lt   20 items   List could have better performance  based on this test HashSet vs  List performance  HashSet lt int gt  nums   new HashSet lt int gt    1  2  3  4  5            if  nums Contains value

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A more complicated way    that emulates SQL s  IN    public static class Ext           public static bool In lt T gt  this T t params T   values           foreach  T value in values                if  t Equals value                     return true                                  return false           if  value In 1 2                    But go for the standard way  it s more readable   EDIT  a better solution  according to  Kobi s suggestion   public static class Ext           public static bool In lt T gt  this T t params T   values           return values Contains t

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Using Linq   if new int    1  2  Contains value    But I d have to think that your original if is faster

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Is this what you are looking for    if  new int     1  2  3  4  5   Contains value

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Using Extension Methods   public static class ObjectExtension       public static bool In this object obj  params object   objects                if  objects    null    obj    null              return false          object found   objects FirstOrDefault o   gt  o GetType   Equals obj GetType     amp  amp  o Equals obj            return  found    null             Now you can do this   string role   Admin   if  role In  Admin    Director

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I had the same problem but solved it with a switch statement  switch a value you are switching on    case 1        the code you want to happen  case 2     the code you want to happen  default     return a value

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How about   if  new    1  2  Contains value     It s a hack though     Or if you don t mind creating your own extension method  you can create the following   public static bool In lt T gt  this T obj  params T   args        return args Contains obj       And you can use it like this   if  1 In 1  2

[c#] if statements matching multiple values

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