[Issue 473] New: Arrays should have a way to take out an element or slice

October 31, 2006
Posted by d-bugmail
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d-bugmail
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http://d.puremagic.com/issues/show_bug.cgi?id=473

           Summary: Arrays should have a way to take out an element or slice
           Product: D
           Version: 0.172
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: wbaxter@gmail.com


There should be a simple way to efficiently remove/drop/erase an element or slice from anywhere in an array.

David Medlock proposes this function for taking out one element: (http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D.learn&artnum=5077)

// remove an item from an array
template drop(T)
{
  T drop( inout T[] arr, int which )
  {
    debug if ( which>=arr.length)
        throw new Exception(str.format("Attempt to drop position %s from size
%s",which,arr.length));
    T result = arr[which];
    int max = arr.length-1;
    for (; which < max; which++ ) arr[which]=arr[which+1];
    arr.length= max;
    return result;
  }
}

Which Chris Nicholson-Sauls timed to be significantly faster than the
alternative using slices:
   a = a[0..n] ~ a[n+1..length];

(http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D.learn&artnum=5099)


A generalization of David's function to drop a range is straightforward.

Sean Kelly proposed it might be worth trying out an implementation using
memmove  instead of a loop.
(http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D.learn&artnum=5100)

A good syntax for this may be to mimick associative arrays, and use "remove()".

   int[] a = [0,1,2,3,4,5];
   a.remove(3); // a now [0,1,2,4,5]
   a.remove(0,3); // a now [4,5]

An alternative, more integrated syntax would be to allow the use of assignment of void.  Then slice syntax could be used directly.

   a[2..4] = void;  // removes a[2] and a[3]

This would require some modification of opSlice methods, or introduction of new ones, like opIndexRemove, opSliceRemove.


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