Re: Fastest Way to Append Multiple Elements to an Array

[MarcelDuchamp via Digitalmars-d-learn]

On Saturday, 20 December 2014 at 00:15:21 UTC, MarcelDuchamp 
wrote:
On Friday, 19 December 2014 at 23:24:13 UTC, zeljkog wrote:
On 19.12.14 23:56, Ali Çehreli wrote:
Can we see the test code please.
Ali

import std.stdio, std.datetime, std.random;

int N = 10_000;
int len = 1000;
int k = 4;

struct S{
  int n1, n2;
//~     this(this){
//~             writeln("this(this)");
//~     }
}

ref T[] append(T, Args...)(ref T[] arr, auto ref Args args)
{
  static if (args.length == 1)
     return arr ~= args[0];
  else{
     arr.length += args.length;
     foreach(i, ref e; args)
        arr[$ - args.length + i] = e;
     return arr;
  }
}

void append1(T)(ref T[] arr, T[] args...)
{
  arr ~= args;
}


void main() {
  S[] arr1 = new S[len];
  S[] arr2, arr3, arr4, arr5;
  foreach (i; 0..len)
     arr1[i] = S(uniform(0, 100), uniform(0, 100));
  auto sw = new StopWatch;

  sw.start();
  foreach(n; 0..N){
     for (int i = 0; i < len; i += k){
        arr2 ~= arr1[i];
        arr2 ~= arr1[i+1];
        arr2 ~= arr1[i+2];
        arr2 ~= arr1[i+3];
//~                     arr2 ~= arr1[i+4];
//~                     arr2 ~= arr1[i+5];
     }
     delete arr2;
  }
  sw.stop();
  long tm = sw.peek.msecs;
  writeln(tm);

  sw.reset();
  sw.start();
  foreach(n; 0..N){
     for (int i = 0; i < len; i += k){
        arr3 ~= [arr1[i], arr1[i+1], arr1[i+2], arr1[i+3]/+  , 
arr1[i+4], arr1[i+5] +/];
     }
     delete arr3;
  }
  sw.stop();
  tm = sw.peek.msecs;
  writeln(tm);

  sw.reset();
  sw.start();
  foreach(n; 0..N){
     for (int i = 0; i < len; i += k){
        arr4.append(arr1[i], arr1[i+1], arr1[i+2], arr1[i+3]/+
 , arr1[i+4], arr1[i+5] +/);
     }
     delete arr4;
  }
  sw.stop();
  tm = sw.peek.msecs;
  writeln(tm);

  sw.reset();
  sw.start();
  foreach(n; 0..N){
     for (int i = 0; i < len; i += k){
        arr5.append1(arr1[i], arr1[i+1], arr1[i+2], 
arr1[i+3]/+   , arr1[i+4], arr1[i+5] +/);
     }
     delete arr5;
  }
  sw.stop();
  tm = sw.peek.msecs;
  writeln(tm);
}

You've forget the array of ref version. (append the address of 
the first data)
And adding S to an array is biased. S is fucking only >>8<< 
bytes. add more data to your struct.

Seriously, do you get what I mean: 'roger this'/'copy that' ?

on an 64 bit OS, to append a 8 bytes struct is the same as 
appending a pointer. It Becommes more interesting to make an 
array of pointer when the struct is bigger.
When I've read your test I just thought: buy a rope man, you 
don't get the thing...
You want to add things but what ? a pointer or full stack of 
values ? 8 bytes it's nothing...