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February 09, 2012
Arrays - Inserting and moving data
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.
February 09, 2012
Re: Arrays - Inserting and moving data
I __believe__ that insertInPlace doesn't shift the elements, but use an
appender allocating another array instead.
Maybe this function do what you want.


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

   void maybe(T)(T[] arr, size_t pos, T value) {
       size_t i;
       for (i = arr.length - 1; i > pos; i--) {
           arr[i] = arr[i-1];
       }
       arr[i] = value;
   }

   maybe(arr, 3, 0);
   maybe(arr, 0, 1);
   assert(arr == [1, 0, 1, 2, 0, 3, 4, 5, 6, 7]);



2012/2/9 MattCodr <matheus_nab@hotmail.com>

> 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.
>
February 09, 2012
Re: Arrays - Inserting and moving data
On Thursday, 9 February 2012 at 12:51:09 UTC, Pedro Lacerda wrote:
> I __believe__ that insertInPlace doesn't shift the elements,

Yes, It appears that it really doesn't shift the array, 
insertInPlace just returns a new array with a new element in n 
position.


> Maybe this function do what you want.
>
>
>   int[] arr = [0,1,2,3,4,5,6,7,8,9];
>
>   void maybe(T)(T[] arr, size_t pos, T value) {
>       size_t i;
>       for (i = arr.length - 1; i > pos; i--) {
>           arr[i] = arr[i-1];
>       }
>       arr[i] = value;
>   }
>


In fact, I usually wrote functions as you did. I just looking for 
a new way to do that with D and Phobos lib.

Thanks,

Matheus.
February 09, 2012
Re: Arrays - Inserting and moving data
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
February 09, 2012
Re: Arrays - Inserting and moving data
On Thu, Feb 09, 2012 at 10:30:22AM -0800, Ali Çehreli wrote:
[...]
> 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.
[...]

Wow! This is really cool. So you *can* have O(1) insertions in the
middle of an array after all. :)

Of course, you probably want to flatten it once in a while to keep
random access cost from skyrocketing. (I'm assuming delegates or
something equivalent are involved in generating the lazy range?)


T

-- 
Give a man a fish, and he eats once. Teach a man to fish, and he will sit forever.
February 09, 2012
Re: Arrays - Inserting and moving data
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.
February 09, 2012
Re: Arrays - Inserting and moving data
On 02/09/2012 11:03 AM, H. S. Teoh wrote:
> On Thu, Feb 09, 2012 at 10:30:22AM -0800, Ali Çehreli wrote:
> [...]
>> 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.
> [...]
>
> Wow! This is really cool. So you *can* have O(1) insertions in the
> middle of an array after all. :)
>
> Of course, you probably want to flatten it once in a while to keep
> random access cost from skyrocketing.

O(1) would be violated only if there are too many actual ranges.

> (I'm assuming delegates or
> something equivalent are involved in generating the lazy range?)

Simpler than that. :) The trick is that chain() returns a range object 
that operates lazily. I have used chain() as an example for finite 
RandomAccessRange types (I used the name 'Together' instead of Chain). 
Search for "Finite RandomAccessRange" here:

  http://ddili.org/ders/d.en/ranges.html

And yes, I note there that the implementation is not O(1). Also look 
under the title "Laziness" in that chapter.

Ali
February 09, 2012
Re: Arrays - Inserting and moving data
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);
}
February 09, 2012
Re: Arrays - Inserting and moving data
On Thursday, 9 February 2012 at 19:49:43 UTC, Timon Gehr wrote:
> Note that this code does the same, but is more efficient if you 
> don't actually need the array:

Yes I know, In fact I need re-think the way I code with this new 
features of D, like ranges for example.

Thanks,

Matheus.
February 10, 2012
Re: Arrays - Inserting and moving data
Am 09.02.2012, 22:03 Uhr, schrieb MattCodr <matheus_nab@hotmail.com>:

> On Thursday, 9 February 2012 at 19:49:43 UTC, Timon Gehr wrote:
>> Note that this code does the same, but is more efficient if you don't  
>> actually need the array:
>
> Yes I know, In fact I need re-think the way I code with this new  
> features of D, like ranges for example.
>
> Thanks,
>
> Matheus.

I know that feeling. I had no exposure to functional programming and  
options like chain never come to my head. Although "map" is a concept that  
I made friends with early.
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