如何从结构数组中删除元素？

Question

I need to remove element from array of structures with, for example value 3 .

Here is my code:

import std.stdio;
import std.range;
import std.array;
import std.string;
import std.algorithm;
import std.conv;

void main()
{
    struct Point
    {
        int order;
        int pos;
        int val;
    }

    Point point;
    Point [] points;



    point.order = 1;
    point.pos = 1;
    point.val = 1;  
    points ~= point;

    point.order = 2;
    point.pos = 4;
    point.val = 2;  
    points ~= point;

    point.order = 3;
    point.pos = 14;
    point.val = 3;  
    points ~= point;    

    point.order = 4;
    point.pos = 24;
    point.val = 1;  
    points ~= point;        

    writeln(points);

}

I thought to do something like:

points.map!(a=>a.val.canFind(3).drop);

But this is do not work. I need to change original points array and drop element from it.

Answer 1

As I understand you want to remove the Points which have a value of 3.

The easiest is to use filter for that:

points = points.filter!(a => a.val != 3).array;

Here it creates a new array but if you don't store the result you can use it lazily without any copy.

If you want to reuse it though and if you do lots of such removing then I recommend that you have a look at std.algorithm:remove which removes an element given its index. Said index can be found using std.algorithm:countUntil for example.

Map is used to apply a transformation on each element of a set, for example [1, 2, 3].map!(x => x*2+1) == [3, 5, 7] . What you defined wasn't a transformation for each element so it couldn't work. Map can't change the length of an array notably, its output is the same length as its input.

EDIT: I forgot to say but this reference might be useful to you https://p0nce.github.io/d-idioms/#Adding-or-removing-an-element-from-arrays