Fastest way to add an Item to an Array

Question

What is the fastest way to add a new item to an existing array   Dim arr As Integer      1  2  3  Dim newItem As Integer   4    I already know that when working with dynamic list of items you should rather use a List  ArrayList or similar IEnumerables  But what to do if you re stuck to legacy code that uses arrays    What I ve tried so far     A  converting to List  add item and convert back Dim list As List Of Integer  arr  list Add newItem  arr   list ToArray     -- gt  duration for adding 100 000 items  33270 msec    B  redim array and add item ReDim Preserve arr arr Length  arr arr Length - 1    newItem   -- gt  duration for adding 100 000 items  9237 msec    C  using Array Resize Array Resize arr  arr Length   1  arr arr Length - 1    newItem   -- gt  duration for adding 100 000 items  1 msec   -- gt  duration for adding 100 000 000 items  1168 msec   A  seems very slow since every time an item is added two conversions of the whole array are done  B  seems faster but still the array is copied once during the ReDim Preserve  C  seems to be the fastest at this point  Is there anything better

User · Answer

Dim arr As Integer      1  2  3  Dim newItem As Integer   4 ReDim Preserve arr  3  arr 3  newItem   for more info Redim

User · Answer

For those who didn t know what next  just add new module file and put  jor code  with my little hacked  supporting  nothing  array  below   Module ArrayExtension      lt Extension   gt        Public Sub Add Of T  ByRef arr As T    item As T          If arr IsNot Nothing Then             Array Resize arr  arr Length   1              arr arr Length - 1    item         Else             ReDim arr 0              arr 0    item         End If      End Sub End Module

User · Answer

Not very clean but it works     Dim arr As Integer      1  2  3  Dim newItem As Integer   4  arr   arr Concat  newItem   ToArray

User · Answer

Case C  is the fastest  Having this as an extension   Public Module MyExtensions      lt Extension   gt        Public Sub Add Of T  ByRef arr As T    item As T          Array Resize arr  arr Length   1          arr arr Length - 1    item     End Sub End Module   Usage   Dim arr As Integer      1  2  3  Dim newItem As Integer   4 arr Add newItem     -- gt  duration for adding 100 000 items  1 msec   -- gt  duration for adding 100 000 000 items  1168 msec

User · Answer

It depends on how often you insert or read  You can increase the array by more than one if needed   numberOfItems              If numberOfItems 1  gt   arr Length Then     Array Resize arr  arr Length   10  End If  arr numberOfItems    newItem numberOfItems    1   Also for A  you only need to get the array if needed   Dim list As List Of Integer  arr    Do this only once  keep a reference to the list                                     If you create a new List everything you add an item then this will never be fast        list Add newItem  arrayWasModified   True         Function GetArray        If arrayWasModified Then         arr   list ToArray       End If      Return Arr End Function   If you have the time  I suggest you convert it all to List and remove arrays     My code might not compile

[arrays] Fastest way to add an Item to an Array

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