How to delete an element from a Slice in Golang

Question

fmt Println  Enter position to delete     fmt Scanln  amp pos   new arr    make   int   len arr  - 1   k    0 for i    0  i  lt   len arr  - 1         if i    pos           new arr i    arr k          k           i         else           k            for i    0  i  lt   len arr  - 1   i         fmt Println new arr i       I am using this command to delete an element from a Slice but it is not working  please suggest

User · Answer

here is the playground example with pointers in it  https   play golang org p uNpTKeCt0sH  package main  import        fmt     type t struct       a int     b string    func  tt  t  String   string      return fmt Sprintf    d  s    tt a  tt b     func remove slice    t  i int     t     copy slice i    slice i 1      return slice  len slice -1     func main         a       t  amp t 1   a     amp t 2   b     amp t 3   c     amp t 4   d     amp t 5   e     amp t 6   f        k    a 3      a   remove a  3      fmt Printf   v       v   a  k

User · Answer

To remove an element from the middle of a slice  preserving the order of the remaining elements  use copy to slide the higher-numbered elements down by one to fill the gap  func remove slice   int  i int    int     copy slice i    slice i 1      return slice  len slice -1       If it is not necessary to preserve the order  we can simply move the last element to the gap  func remove slice   int  i int    int     slice i    slice len slice -1    return slice  len slice -1

User · Answer

From the book The Go Programming Language     To remove an element from the middle of a slice  preserving the order   of the remaining elements  use copy to slide the higher-numbered   elements down by one to fill the gap   func remove slice   int  i int    int     copy slice i    slice i 1      return slice  len slice -1

User · Answer

The best way to do it is to use the append function  package main  import        quot fmt quot     func main         x      int 4  5  6  7  88      fmt Println x      x   append x  2   x 4        deletes 6 and 7     fmt Println x     https   play golang org p -EEFCsqse4u

User · Answer

I take the below approach to remove the item in slice  This helps in readability for others  And also immutable   func remove items   string  item string    string       newitems      string        for    i    range items           if i    item               newitems   append newitems  i                       return newitems

User · Answer

Find a way here without relocating   changes order  a      string  quot A quot    quot B quot    quot C quot    quot D quot    quot E quot   i    2     Remove the element at index i from a  a i    a len a -1     Copy last element to index i  a len a -1     quot  quot       Erase last element  write zero value   a   a  len a -1       Truncate slice   fmt Println a      A B E D    keep order  a      string  quot A quot    quot B quot    quot C quot    quot D quot    quot E quot   i    2     Remove the element at index i from a  copy a i    a i 1       Shift a i 1   left one index  a len a -1     quot  quot         Erase last element  write zero value   a   a  len a -1         Truncate slice   fmt Println a      A B D E

User · Answer

This is how you Delete From a slice the idiomatic way  You don t need to build a function it is built into the append  Try it here https   play golang org p QMXn9-6gU5P z      int 9  8  7  6  5  3  2  1  0  fmt Println z     will print Answer  9 8 7 6 5 3 2 1 0   z   append z  2   z 4       fmt Println z      will print Answer  9 8 5 3 2 1 0

User · Answer

This is a little strange to see but most answers here are dangerous and gloss over what they are actually doing  Looking at the original question that was asked about removing an item from the slice a copy of the slice is being made and then it s being filled  This ensures that as the slices are passed around your program you don t introduce subtle bugs   Here is some code comparing users answers in this thread and the original post  Here is a go playground to mess around with this code in   Append based removal  package main  import        fmt     func RemoveIndex s   int  index int    int       return append s  index   s index 1          func main         all      int 0  1  2  3  4  5  6  7  8  9      fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      removeIndex    RemoveIndex all  5       fmt Println  all     all     0 1 2 3 4 6 7 8 9 9      fmt Println  removeIndex     removeIndex     0 1 2 3 4 6 7 8 9       removeIndex 0    999     fmt Println  all     all     999 1 2 3 4 6 7 9 9      fmt Println  removeIndex     removeIndex     999 1 2 3 4 6 7 8 9      In the above example you can see me create a slice and fill it manually with numbers 0 to 9  We then remove index 5 from all and assign it to remove index  However when we go to print out all now we see that it has been modified as well  This is because slices are pointers to an underlying array  Writing it out to removeIndex causes all to be modified as well with the difference being all is longer by one element that is no longer reachable from removeIndex  Next we change a value in removeIndex and we can see all gets modified as well  Effective go goes into some more detail on this   The following example I won t go into but it does the same thing for our purposes  And just illustrates that using copy is no different   package main  import        fmt     func RemoveCopy slice   int  i int    int       copy slice i    slice i 1        return slice  len slice -1     func main         all      int 0  1  2  3  4  5  6  7  8  9      fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      removeCopy    RemoveCopy all  5       fmt Println  all     all     0 1 2 3 4 6 7 8 9 9      fmt Println  removeCopy     removeCopy     0 1 2 3 4 6 7 8 9       removeCopy 0    999     fmt Println  all     all     99 1 2 3 4 6 7 9 9      fmt Println  removeCopy     removeCopy     999 1 2 3 4 6 7 8 9      The questions original answer  Looking at the original question it does not modify the slice that it s removing an item from  Making the original answer in this thread the best so far for most people coming to this page   package main  import        fmt     func OriginalRemoveIndex arr   int  pos int    int       new arr    make   int   len arr  - 1       k    0     for i    0  i  lt   len arr  - 1             if i    pos               new arr i    arr k              k             else               k                     i              return new arr    func main         all      int 0  1  2  3  4  5  6  7  8  9      fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      originalRemove    OriginalRemoveIndex all  5       fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      fmt Println  originalRemove     originalRemove     0 1 2 3 4 6 7 8 9       originalRemove 0    999     fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      fmt Println  originalRemove     originalRemove     999 1 2 3 4 6 7 8 9      As you can see this output acts as most people would expect and likely what most people want  Modification of originalRemove doesn t cause changes in all and the operation of removing the index and assigning it doesn t cause changes as well  Fantastic   This code is a little lengthy though so the above can be changed to this   A correct answer  package main  import        fmt     func RemoveIndex s   int  index int    int       ret    make   int  0      ret   append ret  s  index          return append ret  s index 1          func main         all      int 0  1  2  3  4  5  6  7  8  9      fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      removeIndex    RemoveIndex all  5       fmt Println  all     all     0 1 2 3 4 5 6 7 8 9      fmt Println  removeIndex     removeIndex     0 1 2 3 4 6 7 8 9       removeIndex 0    999     fmt Println  all     all     0 1 2 3 4 5 6 7 9 9      fmt Println  removeIndex     removeIndex     999 1 2 3 4 6 7 8 9      Almost identical to the original remove index solution however we make a new slice to append to before returning

User · Answer

Order matters  If you want to keep your array ordered  you have to shift all of the elements at the right of the deleting index by one to the left  Hopefully  this can be done easily in Golang   func remove slice   int  s int    int       return append slice  s   slice s 1           However  this is inefficient because you may end up with moving all of the elements  which is costy   Order is not important  If you do not care about ordering  you have the much faster possibility to swap the element to delete with the one at the end of the slice and then return the n-1 first elements   func remove s   int  i int    int       s len s -1   s i    s i   s len s -1      return s  len s -1      With the reslicing method  emptying an array of 1 000 000 elements take 224s  with this one it takes only 0 06ns  I suspect that internally  go only changes the length of the slice  without modifying it   Edit 1  Quick notes based on the comments below  thanks to them      As the purpose is to delete an element  when the order does not matter a single swap is needed  the second will be wasted    func remove s   int  i int    int       s i    s len s -1         We do not need to put s i  at the end  as it will be discarded anyway     return s  len s -1      Also  this answer does not perform bounds-checking  It expects a valid index as input  This means that negative values or indices that are greater or equal to len s  will cause Go to panic  Slices and arrays being 0-indexed  removing the n-th element of an array implies to provide input n-1  To remove the first element  call remove s  0   to remove the second  call remove s  1   and so on and so forth

User · Answer

No need to check every single element unless you care contents and you can utilize slice append  try it out  pos    0 arr      int 1  2  3  4  5  6  7  9  fmt Println  input your position   fmt Scanln  amp pos     you need to check if negative input as well    if  pos  lt  len arr        arr   append arr  pos   arr pos 1         else       fmt Println  position invalid

User · Answer

Remove one element from the Slice  this is called  re-slicing     package main  import        fmt     func RemoveIndex s   int  index int    int       return append s  index   s index 1          func main         all      int 0  1  2  3  4  5  6  7  8  9      fmt Println all     0 1 2 3 4 5 6 7 8 9      all   RemoveIndex all  5      fmt Println all     0 1 2 3 4 6 7 8 9

User · Answer

Maybe this code will help   It deletes item with a given index   Takes the array  and the index to delete and returns a new array pretty much like append function   func deleteItem arr   int  index int    int    if index  lt  0    index  gt   len arr       return   int -1           for i    index  i  lt  len arr  -1  i          arr i    arr i   1              return arr  len arr -1      Here you can play with the code   https   play golang org p aX1Qj40uTVs

User · Answer

Minor point  code golf   but in the case where order does not matter you don t need to swap the values  Just overwrite the array position being removed with a duplicate of the last position and then return a truncated array    func remove s   int  i int    int       s i    s len s -1      return s  len s -1      Same result

User · Answer

Maybe you can try this method      DelEleInSlice delete an element from slice by index     - arr  the reference of slice     - index  the index of element will be deleted func DelEleInSlice arr interface    index int        vField    reflect ValueOf arr      value    vField Elem       if value Kind      reflect Slice    value Kind      reflect Array           result    reflect AppendSlice value Slice 0  index   value Slice index 1  value Len             value Set result            Usage   arrInt      int 0  1  2  3  4  5  arrStr      string  0    1    2    3    4    5   DelEleInSlice  amp arrInt  3  DelEleInSlice  amp arrStr  4  fmt Println arrInt  fmt Println arrStr    Result   0  1  2  4  5  0    1    2    3    5

[go] How to delete an element from a Slice in Golang

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