How do I remove an item from a stl vector with a certain value

Question

I was looking at the API documentation for stl vector  and noticed there was no method on the vector class that allowed the removal of an element with a certain value  This seems like a common operation  and it seems odd that there s no built in way to do this

User · Answer

If you have an unsorted vector  then you can simply swap with the last vector element then resize     With an ordered container  you ll be best off with  std  vector  erase     Note that there is a std  remove   defined in  lt algorithm gt   but that doesn t actually do the erasing    Read the documentation carefully

User · Answer

Use the global method std  remove with the begin and end iterator  and then use std  vector erase to actually remove the elements   Documentation links std  remove http   www cppreference com cppalgorithm remove html std  vector erase http   www cppreference com cppvector erase html  std  vector lt int gt  v  v push back 1   v push back 2      Vector should contain the elements 1  2    Find new end iterator std  vector lt int gt   iterator newEnd   std  remove v begin    v end    1      Erase the  removed  elements  v erase newEnd  v end        Vector should now only contain 2   Thanks to Jim Buck for pointing out my error

User · Answer

The other answers cover how to do this well  but I thought I d also point out that it s not really odd that this isn t in the vector API  it s inefficient  linear search through the vector for the value  followed by a bunch of copying to remove it   If you re doing this operation intensively  it can be worth considering std  set instead for this reason

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If you want to remove an item  the following will be a bit more efficient   std  vector lt int gt  v    auto it   std  find v begin    v end    5   if it    v end        v erase it     or you may avoid overhead of moving the items if the order does not matter to you   std  vector lt int gt  v   auto it   std  find v begin    v end    5    if  it    v end        using std  swap        swap the one to be removed with the last element      and remove the item at the end of the container      to prevent moving all items after  5  by one   swap  it  v back       v pop back

User · Answer

Two ways are there by which you can use to erase an item particularly   lets take a vector  std    vector  lt  int  gt  v  v push back 10   v push back 20   v push back 30   v push back 40   v push back 40   v push back 50     1  Non efficient way   Although it seems to be quite efficient but it s not because erase function delets the elements and shifts all the elements towards left by 1   so its complexity will be O n 2   std    vector  lt  int  gt     iterator itr   v begin    int value   40  while   itr    v end          if  itr    value              v erase itr           else          itr      2  Efficient way   RECOMMENDED     It is also known as ERASE - REMOVE idioms       std  remove transforms the given range into a range with all the elements that compare not equal to given element shifted to the start of the container  So  actually don t remove the matched elements  It just shifted the non matched to starting and gives an iterator to new valid end  It just requires O n  complexity    output of the remove algorithm is     10 20 30 50 40 50    as return type of remove is iterator to the new end of that range   template  lt class ForwardIterator  class T gt    ForwardIterator remove  ForwardIterator first  ForwardIterator last  const T amp  val     Now use vector   s erase function to delete elements from the new end to old end of the vector  It requires O 1  time   v erase   std    remove  v begin     v end     element     v end         so this method work in O n

User · Answer

From c  20   A non-member function introduced std  erase  which takes the vector and value to be removed as inputs   ex   std  vector lt int gt  v    90 80 70 60 50   std  erase v 50

User · Answer

If you want to do it without any extra includes    vector lt IComponent  gt  myComponents    assume it has items in it already  void RemoveComponent IComponent  componentToRemove        IComponent  juggler       if  componentToRemove    NULL                for  int currComponentIndex   0  currComponentIndex  lt  myComponents size    currComponentIndex                          if  componentToRemove    myComponents currComponentIndex                                   Since we don t care about order  swap with the last element  then delete it                  juggler   myComponents currComponentIndex                   myComponents currComponentIndex    myComponents myComponents size   - 1                   myComponents myComponents size   - 1    juggler                     Remove it from memory and let the vector know too                  myComponents pop back                    delete juggler

User · Answer

A shorter solution  which doesn t force you to repeat the vector name 4 times  would be to use Boost    include  lt boost range algorithm ext erase hpp gt           boost  remove erase vec  int to remove     See http   www boost org doc libs 1 64 0 libs range doc html range reference algorithms new remove erase html

User · Answer

C   community has heard your request         C   20 provides an easy way of doing it now   It gets as simple as     include  lt vector gt      vector lt int gt  cnt 5  0  2  8  0  7   std  erase cnt  0     You should check out std  erase and std  erase if   Not only will it remove all elements of the value  here  0    it will do it in O n  time complexity  Which is the very best you can get   If your compiler does not support C   20  you should use erase-remove idiom    include  lt algorithm gt      vec erase std  remove vec begin    vec end    0   vec end

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See also std  remove if to be able to use a predicate     Here s the example from the link above   vector lt int gt  V  V push back 1   V push back 4   V push back 2   V push back 8   V push back 5   V push back 7    copy V begin    V end    ostream iterator lt int gt  cout                The output is  1 4 2 8 5 7   vector lt int gt   iterator new end        remove if V begin    V end                   compose1 bind2nd equal to lt int gt     0                          bind2nd modulus lt int gt     2     V erase new end  V end      1   copy V begin    V end    ostream iterator lt int gt  cout                The output is  1 5 7

User · Answer

std  remove does not actually erase the element from the container  but it does return the new end iterator which can be passed to container type  erase to do the REAL removal of the extra elements that are now at the end of the container   std  vector lt int gt  vec        put in some values    int int to remove   n  vec erase std  remove vec begin    vec end    int to remove   vec end

[c++] How do I remove an item from a stl vector with a certain value?

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