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digitalmars.D.learn - Using zip to copy subarray into another

reply "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
I have code that attempts to copy a slice of one array into
another using zip. However, the array is not updated.   I am
guessing this is because modifying the returned tuple does not
modify the actual arrays.

Is there any way to do this.


import std.stdio;
import std.range;

void main( string[] args ) {
    int[] array1 = [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1];
    int[] array2 = [2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2];

    foreach( ref a; zip(array1[2..$], array2[4..6] ) ) {
      a[0] = a[1];
    }

    foreach( int v; array1 ) write(v, ",");
}

prints 1,1,1,1,...

Thanks
Craig
Aug 13 2013
next sibling parent reply "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Tuesday, August 13, 2013 21:22:24 Craig Dillabaugh wrote:

 I have code that attempts to copy a slice of one array into
 another using zip. However, the array is not updated. I am
 guessing this is because modifying the returned tuple does not
 modify the actual arrays.
 
 Is there any way to do this.


Why not just use std.algorithm.copy, or even just assigning one array to the 
other? e.g.

dest[2 .. 5] = src[1 .. 4];

- Jonathan M Davis
Aug 13 2013
parent reply "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
On Tuesday, 13 August 2013 at 19:50:37 UTC, Jonathan M Davis
wrote:

 On Tuesday, August 13, 2013 21:22:24 Craig Dillabaugh wrote:

 I have code that attempts to copy a slice of one array into
 another using zip. However, the array is not updated. I am
 guessing this is because modifying the returned tuple does not
 modify the actual arrays.
 
 Is there any way to do this.


 Why not just use std.algorithm.copy, or even just assigning one 
 array to the
 other? e.g.

 dest[2 .. 5] = src[1 .. 4];

 - Jonathan M Davis


These work reasonably well and I will likely use your suggestions
here.

The one thing I get with zip that I lose using std.algorithm.copy
or straight assignment of the slices is that it handles
mismatches in slice sizes automatically (it stops as soon as
either slice is exhausted).

For example

    copy(array2[4..8], array1[9..$]);

where array1 had 10 elements fails because it copies data off the
end of array1, and if I use straight assignment the slices must
be the same length.

Craig
Aug 13 2013
parent reply "John Colvin" <john.loughran.colvin gmail.com> writes:
On Tuesday, 13 August 2013 at 20:23:00 UTC, Craig Dillabaugh 
wrote:

 On Tuesday, 13 August 2013 at 19:50:37 UTC, Jonathan M Davis
 wrote:

 On Tuesday, August 13, 2013 21:22:24 Craig Dillabaugh wrote:

 I have code that attempts to copy a slice of one array into
 another using zip. However, the array is not updated. I am
 guessing this is because modifying the returned tuple does not
 modify the actual arrays.
 
 Is there any way to do this.


 Why not just use std.algorithm.copy, or even just assigning 
 one array to the
 other? e.g.

 dest[2 .. 5] = src[1 .. 4];

 - Jonathan M Davis


 These work reasonably well and I will likely use your 
 suggestions
 here.

 The one thing I get with zip that I lose using 
 std.algorithm.copy
 or straight assignment of the slices is that it handles
 mismatches in slice sizes automatically (it stops as soon as
 either slice is exhausted).

 For example

    copy(array2[4..8], array1[9..$]);

 where array1 had 10 elements fails because it copies data off 
 the
 end of array1, and if I use straight assignment the slices must
 be the same length.

 Craig



warning: untested!

void myCopy(T)(T[] a, T[] b)
{
     auto possible = min(a.length, b.length);
     a[0 .. possible] = b[0 .. possible];
}

myCopy(array2[4..8], array1[9..$]);

Arrays only atm, but you could quite easily spruce that up in to 
something much more generic.
Aug 13 2013
parent "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
On Tuesday, 13 August 2013 at 21:10:53 UTC, John Colvin wrote:

 On Tuesday, 13 August 2013 at 20:23:00 UTC, Craig Dillabaugh 
 wrote:

 On Tuesday, 13 August 2013 at 19:50:37 UTC, Jonathan M Davis
 wrote:

 On Tuesday, August 13, 2013 21:22:24 Craig Dillabaugh wrote:

 I have code that attempts to copy a slice of one array into
 another using zip. However, the array is not updated. I am
 guessing this is because modifying the returned tuple does 
 not
 modify the actual arrays.
 
 Is there any way to do this.


 Why not just use std.algorithm.copy, or even just assigning 
 one array to the
 other? e.g.

 dest[2 .. 5] = src[1 .. 4];

 - Jonathan M Davis


 These work reasonably well and I will likely use your 
 suggestions
 here.

 The one thing I get with zip that I lose using 
 std.algorithm.copy
 or straight assignment of the slices is that it handles
 mismatches in slice sizes automatically (it stops as soon as
 either slice is exhausted).

 For example

   copy(array2[4..8], array1[9..$]);

 where array1 had 10 elements fails because it copies data off 
 the
 end of array1, and if I use straight assignment the slices must
 be the same length.

 Craig



 warning: untested!

 void myCopy(T)(T[] a, T[] b)
 {
     auto possible = min(a.length, b.length);
     a[0 .. possible] = b[0 .. possible];
 }

 myCopy(array2[4..8], array1[9..$]);

 Arrays only atm, but you could quite easily spruce that up in 
 to something much more generic.


Thanks. I ended up using something along these lines in my code
(although I didn't write a nice generic function as you have
done).
Aug 14 2013
prev sibling parent reply Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:
On 08/13/2013 09:22 PM, Craig Dillabaugh wrote:

 I have code that attempts to copy a slice of one array into
 another using zip. However, the array is not updated.   I am
 guessing this is because modifying the returned tuple does not
 modify the actual arrays.
 
 Is there any way to do this.


Try lockstep instead of zip.  See:
http://d.puremagic.com/issues/show_bug.cgi?id=8155#c8

... for more info on the reasons why zip doesn't work here.
Aug 13 2013
parent "Craig Dillabaugh" <cdillaba cg.scs.carleton.ca> writes:
On Tuesday, 13 August 2013 at 21:37:28 UTC, Joseph Rushton
Wakeling wrote:
clip.

 Try lockstep instead of zip.  See:
 http://d.puremagic.com/issues/show_bug.cgi?id=8155#c8

 ... for more info on the reasons why zip doesn't work here.


While I've now solved my problem using a slightly different
method, you are right lockstep would have also likely made a good
solution.

Thanks.
Aug 14 2013