Re: Arrays - Inserting and moving data

[Timon Gehr]

On 02/09/2012 08:20 PM, MattCodr wrote:
On Thursday, 9 February 2012 at 18:30:22 UTC, Ali Çehreli wrote:
On 02/09/2012 03:47 AM, MattCodr wrote:
I have a doubt about the best way to insert and move (not replace) some
data on an array.
For example,

In some cases if I want to do action above, I do a loop moving the data
until the point that I want and finally I insert the new data there.


In D I did this:

begin code
.
.
.
int[] arr = [0,1,2,3,4,5,6,7,8,9];

arr.insertInPlace(position, newValue);
arr.popBack();
.
.
.
end code


After the insertInPlace my array changed it's length to 11, so I use
arr.popBack(); to keep the array length = 10;

The code above is working well, I just want know if is there a better
way?

Thanks,

Matheus.

Most straightforward that I know of is the following:

arr = arr[0 .. position] ~ [ newValue ] ~ arr[position + 1 .. $];

But if you don't actually want to modify the data, you can merely
access the elements in-place by std.range.chain:

import std.stdio;
import std.range;

void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;

auto r = chain(arr[0 .. position], [ newValue ], arr[position + 1 .. $]);
writeln(r);
}

'r' above is a lazy range that just provides access to the three
ranges given to it. 'arr' does not change in any way.

Ali

Hi Ali,

You gave me a tip with this "chain" feature.

I changed a few lines of your code, and it worked as I wanted:


import std.stdio;
import std.range;
import std.array;

void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;

auto r = chain(arr[0 .. position], [ newValue ], arr[position .. $-1]);
arr = array(r);

foreach(int i; arr)
writefln("%d", i);
}


Thanks,

Matheus.


Note that this code does the same, but is more efficient if you don't 
actually need the array:


import std.stdio;
import std.range;
import std.array;

void main()
{
    int[] arr = [0,1,2,3,4,5,6,7,8,9];
    immutable position = arr.length / 2;
    immutable newValue = 42;

    auto r = chain(arr[0 .. position], [ newValue ], arr[position .. $-1]);

    foreach(i; r)
        writefln("%d", i);
}