How to replace list item in best way

Question

if  listofelements Contains valueFieldValue ToString           listofelements listofelements IndexOf valueFieldValue ToString       value ToString        I have replaced like above   Is there any other bestway to place compare than this one

User · Answer

Following rokkuchan s answer  just a little upgrade   List lt string gt  listOfStrings   new List lt string gt    abc    123    ghi     int index   listOfStrings FindIndex ind   gt  ind Equals  123     if  index  gt  -1      listOfStrings index      def

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Why not use the extension methods  Consider the following code          var intArray   new int     0  1  1  2  3  4               Replaces the first occurance and returns the index         var index   intArray Replace 1  0               0  0  1  2  3  4   index 1          var stringList   new List lt string gt     quot a quot    quot a quot    quot c quot    quot d quot            stringList ReplaceAll  quot a quot    quot b quot                 quot b quot    quot b quot    quot c quot    quot d quot             var intEnum   intArray Select x   gt  x           intEnum   intEnum Replace 0  1               0  0  1  2  3  4    gt   1  1  1  2  3  4    No code duplication There is no need to type long linq expressions There is no need for additional usings  The source code  namespace System Collections Generic       public static class Extensions               public static int Replace lt T gt  this IList lt T gt  source  T oldValue  T newValue                        if  source    null                  throw new ArgumentNullException nameof source                 var index   source IndexOf oldValue               if  index    -1                  source index    newValue              return index                     public static void ReplaceAll lt T gt  this IList lt T gt  source  T oldValue  T newValue                        if  source    null                  throw new ArgumentNullException nameof source                 int index   -1              do                               index   source IndexOf oldValue                   if  index    -1                      source index    newValue                while  index    -1                       public static IEnumerable lt T gt  Replace lt T gt  this IEnumerable lt T gt  source  T oldValue  T newValue                        if  source    null                  throw new ArgumentNullException nameof source                 return source Select x   gt  EqualityComparer lt T gt  Default Equals x  oldValue    newValue   x                      The first two methods have been added to change the objects of reference types in place  Of course  you can use just the third method for all types  P S  Thanks to mike s observation  I ve added the ReplaceAll method

User · Answer

You are accessing your list twice to replace one element  I think simple for loop should be enough   var key   valueFieldValue ToString    for  int i   0  i  lt  listofelements Count  i          if  listofelements i     key                listofelements i    value ToString            break

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I don t if it is best or not but you can use it also  List lt string gt  data   new List lt string gt   new string        Computer    A    B    Computer    B    A      int   indexes   Enumerable Range 0  data Count  Where                   i   gt  data i      Computer   ToArray    Array ForEach indexes  i   gt  data i     Calculator

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i find best for do it fast and simple   find ur item in list  var d   Details Where x   gt  x ProductID    selectedProduct ID  SingleOrDefault     make clone from current  OrderDetail dd   d   Update ur clone  dd Quantity     find index in list  int idx   Details IndexOf d    remove founded item in  1     Details Remove d    insert   if  idx  gt  -1        Details Insert idx  dd     else       Details Insert Details Count  dd

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You can use the next extensions which are based on a predicate condition             lt summary gt          Find an index of a first element that satisfies  lt paramref name  match   gt           lt  summary gt           lt typeparam name  T  gt Type of elements in the source collection lt  typeparam gt           lt param name  this  gt This lt  param gt           lt param name  match  gt Match predicate lt  param gt           lt returns gt Zero based index of an element  -1 if there is not such matches lt  returns gt      public static int IndexOf lt T gt  this IList lt T gt   this  Predicate lt T gt  match                 this ThrowIfArgumentIsNull            match ThrowIfArgumentIsNull             for  int i   0  i  lt   this Count    i              if  match  this i                    return i           return -1                  lt summary gt          Replace the first occurance of an oldValue which satisfies the  lt paramref name  removeByCondition   gt  by a newValue          lt  summary gt           lt typeparam name  T  gt Type of elements of a target list lt  typeparam gt           lt param name  this  gt Source collection lt  param gt           lt param name  removeByCondition  gt A condition which decides is a value should be replaced or not lt  param gt           lt param name  newValue  gt A new value instead of replaced lt  param gt           lt returns gt This lt  returns gt      public static IList lt T gt  Replace lt T gt  this IList lt T gt   this  Predicate lt T gt  replaceByCondition  T newValue                 this ThrowIfArgumentIsNull            removeByCondition ThrowIfArgumentIsNull             int index    this IndexOf replaceByCondition           if  index    -1               this index    newValue           return  this                  lt summary gt          Replace all occurance of values which satisfy the  lt paramref name  removeByCondition   gt  by a newValue          lt  summary gt           lt typeparam name  T  gt Type of elements of a target list lt  typeparam gt           lt param name  this  gt Source collection lt  param gt           lt param name  removeByCondition  gt A condition which decides is a value should be replaced or not lt  param gt           lt param name  newValue  gt A new value instead of replaced lt  param gt           lt returns gt This lt  returns gt      public static IList lt T gt  ReplaceAll lt T gt  this IList lt T gt   this  Predicate lt T gt  replaceByCondition  T newValue                 this ThrowIfArgumentIsNull            removeByCondition ThrowIfArgumentIsNull             for  int i   0  i  lt   this Count    i              if  replaceByCondition  this i                     this i    newValue           return  this          Notes   - Instead of ThrowIfArgumentIsNull extension  you can use a general approach like   if  argName    null  throw new ArgumentNullException nameof argName      So your case with these extensions can be solved as    string targetString   valueFieldValue ToString    listofelements Replace x   gt  x Equals targetString   value ToString

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Or  building on Rusian L  s suggestion  if the item you re searching for can be in the list more than once     Extension    public void ReplaceAll lt T gt  List lt T gt  input  T search  T replace        int i   0      do           i   input FindIndex i  s   gt  EqualityComparer lt T gt  Default Equals s  search             if  i  gt  -1                FileSystem input i    replace              continue                     break          while  true

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You can use lambda expression like this   int index   listOfElements FindIndex item   gt  item Id    id     if  index    -1         listOfElements index    newValue

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You could make it more readable and more efficient   string oldValue   valueFieldValue ToString    string newValue   value ToString    int index   listofelements IndexOf oldValue   if index    -1      listofelements index    newValue    This asks only once for the index  Your approach uses Contains first which needs to loop all items in the worst case   then you re using IndexOf which needs to enumerate the items again

User · Answer

Use Lambda to find the index in the List and use this index to replace the list item   List lt string gt  listOfStrings   new List lt string gt    abc    123    ghi    listOfStrings listOfStrings FindIndex ind  gt ind Equals  123         def

User · Answer

Use FindIndex and lambda to find and replace your values   int j   listofelements FindIndex i   gt  i Contains valueFieldValue ToString        Finds the item index  lstString j    lstString j  Replace valueFieldValue ToString    value ToString       Replaces the item by new value

[c#] How to replace list item in best way

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