Re: std way to remove multiple indices from an array at once

[Steven Schveighoffer via Digitalmars-d-learn]

On 12/20/17 6:01 PM, aliak wrote:
Hi, is there a way to remove a number of elements from an array by a 
range of indices in the standard library somewhere?

I wrote one (code below), but I'm wondering if there's a better way?

Also, can the below be made more efficient?

auto without(T, R)(T[] array, R indices) if (isForwardRange!R && 
isIntegral!(ElementType!R) && !isInfinite!R) {
     T[] newArray;
     ElementType!R start = 0;
     foreach (i; indices) {
         newArray ~= array[start .. i];
         start = i + 1;
     }
     newArray ~= array[start .. $];
     return newArray;
}

// Usage
long[] aa = [1, 2, 3, 4]
aa = aa.without([1, 3])

Thanks!

I'm assuming here indices is sorted? Because it appears you expect that 
in your code. However, I'm going to assume it isn't sorted at first.

Now:

import std.range;
import std.algorithm;

auto indices = [1,2,3,4];
aa = aa.enumerate.filter!(a => !indicies.canFind(a[0])).map(a => 
a[1]).array;

Now, this is going to be O(n^2), but if indices is sorted, you could use 
binary search:

auto sortedIdxs = indices.assumeSorted; // also could be = indices.sort()

arr = arr.enumerate.filter!(a => !sortedIdxs.contains(a[0])).map(a => 
a[1]).array;

Complexity would be O(n lg(n))

It's not going to be as good as hand-written code, complexity wise, but 
it's definitely shorter to write :)

-Steve