digitalmars.D.learn - We have slices, do we have Strides?

Kai Meyer (11/11) Aug 08 2011 I have a problem I'd really like to use Strides for to simplify my code....

Jonathan M Davis (2/16) Aug 08 2011 Would std.range.stride work for you?

Kai Meyer (8/24) Aug 08 2011 It would, if there was a way to give it an offset:

Jonathan M Davis (13/42) Aug 08 2011 The simplest way is to just pop off the appropriate number of elements f...
Steven Schveighoffer (3/29) Aug 08 2011 -Steve

Jonathan M Davis (3/34) Aug 08 2011 LOL. Yes. Since he's dealing with arrays rather than a generic input ran...
Kai Meyer (2/33) Aug 09 2011 Awesome :) Thanks Steve!
Kai Meyer (17/48) Aug 09 2011 Doh, how do I extract the array from the return value of stride?

Steven Schveighoffer (22/74) Aug 09 2011 Two options, first, you can change do_something to accept a range

Kai Meyer (2/80) Aug 09 2011 Both of those solutions worked, thanks :)

Kai Meyer <kai unixlords.com> writes:

I have a problem I'd really like to use Strides for to simplify my code. 
Currently, I do this:
         foreach(n; 0..chunks)
             comp_arr[n] = values[(n * step_size) + n]
         if(!all_same(comp_arr, comp_arr[0]))

It would eliminate an entire 2 lines of code for each time I want 
strides, to be able to do this:
         if(!all_same(bytes[i..$..step_size])

Meaning, start with i, grab all elements at i + block_size * n until 
block_size * n > bytes.length. Right?

-Kai Meyer

Aug 08 2011

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

 I have a problem I'd really like to use Strides for to simplify my code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))
 
 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])
 
 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n > bytes.length. Right?
 
 -Kai Meyer

Would std.range.stride work for you?

- Jonathan M Davis

Aug 08 2011

Kai Meyer <kai unixlords.com> writes:

On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))

 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])

 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n>  bytes.length. Right?

 -Kai Meyer

 Would std.range.stride work for you?

 - Jonathan M Davis

It would, if there was a way to give it an offset:

int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];
assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
assert(equal(stride(a, 3, 1), [ 2, 5, 8, 11 ][]));
assert(equal(stride(a, 3, 2), [ 3, 6, 9 ][]));
assert(equal(stride(a, 3, 3), [ 4, 7, 10 ][]));

Is that possible?

Aug 08 2011

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))
 
 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])
 
 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n> bytes.length. Right?
 
 -Kai Meyer

 
 Would std.range.stride work for you?
 
 - Jonathan M Davis

 
 It would, if there was a way to give it an offset:
 
 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];
 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a, 3, 1), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a, 3, 2), [ 3, 6, 9 ][]));
 assert(equal(stride(a, 3, 3), [ 4, 7, 10 ][]));
 
 Is that possible?

The simplest way is to just pop off the appropriate number of elements from 
the front. Now, maybe stride should be enhanced to take an offset, but you can 
do it by just popping off the appropriate number of elements first. Another 
option would be drop, if it ends up in the next release:

https://github.com/D-Programming-Language/phobos/pull/147

It would allow you to drop pop the elements from a slice of a which would then 
be passed to stride instead of having to create a slice and pop off the 
elements before calling stride. If it gets into Phobos though, that probably 
makes it so that there's no real need to make stride take an offset. 
Regardless, for the moment, it looks like you need to pop off the appropriate 
number of elements from a (or a slice of a) before passing it to stride if you 
want an offset.

- Jonathan M Davis

Aug 08 2011

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

On Mon, 08 Aug 2011 18:33:55 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my  
 code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))

 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])

 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n>  bytes.length. Right?

 -Kai Meyer

 Would std.range.stride work for you?

 - Jonathan M Davis

 It would, if there was a way to give it an offset:

 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];

fixed:

 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a[1..$], 3), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a[2..$], 3), [ 3, 6, 9 ][]));
 assert(equal(stride(a[3..$], 3), [ 4, 7, 10 ][]));

-Steve

Aug 08 2011

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

 On Mon, 08 Aug 2011 18:33:55 -0400, Kai Meyer <kai unixlords.com> wrote:
 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my
 code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))
 
 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])
 
 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n> bytes.length. Right?
 
 -Kai Meyer

 
 Would std.range.stride work for you?
 
 - Jonathan M Davis

 
 It would, if there was a way to give it an offset:
 
 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];

 
 fixed:
 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a[1..$], 3), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a[2..$], 3), [ 3, 6, 9 ][]));
 assert(equal(stride(a[3..$], 3), [ 4, 7, 10 ][]));


LOL. Yes. Since he's dealing with arrays rather than a generic input range, 
that works great.

- Jonathan M Davis

Aug 08 2011

Kai Meyer <kai unixlords.com> writes:

On 08/08/2011 05:25 PM, Steven Schveighoffer wrote:
 On Mon, 08 Aug 2011 18:33:55 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my
 code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))

 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])

 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n> bytes.length. Right?

 -Kai Meyer

 Would std.range.stride work for you?

 - Jonathan M Davis

 It would, if there was a way to give it an offset:

 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];

 fixed:

 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a[1..$], 3), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a[2..$], 3), [ 3, 6, 9 ][]));
 assert(equal(stride(a[3..$], 3), [ 4, 7, 10 ][]));

 -Steve

Awesome :) Thanks Steve!

Aug 09 2011

Kai Meyer <kai unixlords.com> writes:

On 08/08/2011 05:25 PM, Steven Schveighoffer wrote:
 On Mon, 08 Aug 2011 18:33:55 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my
 code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))

 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])

 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n> bytes.length. Right?

 -Kai Meyer

 Would std.range.stride work for you?

 - Jonathan M Davis

 It would, if there was a way to give it an offset:

 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];

 fixed:

 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a[1..$], 3), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a[2..$], 3), [ 3, 6, 9 ][]));
 assert(equal(stride(a[3..$], 3), [ 4, 7, 10 ][]));

 -Steve

Doh, how do I extract the array from the return value of stride?

import std.range;
int do_something(int[] values)
{
     return values[0];
}
void main(string[] args)
{
         int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];
             do_something(stride(a,3));
}


I get:
moo.d(9): Error: function moo.do_something (int[] values) is not 
callable using argument types (Result)
moo.d(9): Error: cannot implicitly convert expression (stride(a,3LU)) of 
type Result to int[]

Aug 09 2011

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

On Tue, 09 Aug 2011 11:29:52 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 05:25 PM, Steven Schveighoffer wrote:
 On Mon, 08 Aug 2011 18:33:55 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my
 code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))

 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])

 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n> bytes.length. Right?

 -Kai Meyer

 Would std.range.stride work for you?

 - Jonathan M Davis

 It would, if there was a way to give it an offset:

 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];

 fixed:

 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a[1..$], 3), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a[2..$], 3), [ 3, 6, 9 ][]));
 assert(equal(stride(a[3..$], 3), [ 4, 7, 10 ][]));

 -Steve

 Doh, how do I extract the array from the return value of stride?

 import std.range;
 int do_something(int[] values)
 {
      return values[0];
 }
 void main(string[] args)
 {
          int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];
              do_something(stride(a,3));
 }


 I get:
 moo.d(9): Error: function moo.do_something (int[] values) is not  
 callable using argument types (Result)
 moo.d(9): Error: cannot implicitly convert expression (stride(a,3LU)) of  
 type Result to int[]

Two options, first, you can change do_something to accept a range  
(depending on what the real implementation of do_something is, you might  
need to require a random-access range, but that dummy implementation could  
accept any input range, just return x.front):

int do_something(R)(R values) if (isInputRange!R && is(ElementType!R :  
int))
{
    return values.front; // maybe need random access in real code?
}

Second option, convert range to an array.  This incurs a memory allocation  
to create the array:

import std.array;

...
void main(...)
{
    ...
    do_something(array(stride(a, 3)));
}

doc for std.array.array:  
http://www.d-programming-language.org/phobos/std_array.html#array

-Steve

Aug 09 2011

Kai Meyer <kai unixlords.com> writes:

On 08/09/2011 09:37 AM, Steven Schveighoffer wrote:
 On Tue, 09 Aug 2011 11:29:52 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 05:25 PM, Steven Schveighoffer wrote:
 On Mon, 08 Aug 2011 18:33:55 -0400, Kai Meyer <kai unixlords.com> wrote:

 On 08/08/2011 12:55 PM, Jonathan M Davis wrote:
 I have a problem I'd really like to use Strides for to simplify my
 code.
 Currently, I do this:
 foreach(n; 0..chunks)
 comp_arr[n] = values[(n * step_size) + n]
 if(!all_same(comp_arr, comp_arr[0]))

 It would eliminate an entire 2 lines of code for each time I want
 strides, to be able to do this:
 if(!all_same(bytes[i..$..step_size])

 Meaning, start with i, grab all elements at i + block_size * n until
 block_size * n> bytes.length. Right?

 -Kai Meyer

 Would std.range.stride work for you?

 - Jonathan M Davis

 It would, if there was a way to give it an offset:

 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];

 fixed:

 assert(equal(stride(a, 3), [ 1, 4, 7, 10 ][]));
 assert(equal(stride(a[1..$], 3), [ 2, 5, 8, 11 ][]));
 assert(equal(stride(a[2..$], 3), [ 3, 6, 9 ][]));
 assert(equal(stride(a[3..$], 3), [ 4, 7, 10 ][]));

 -Steve

 Doh, how do I extract the array from the return value of stride?

 import std.range;
 int do_something(int[] values)
 {
 return values[0];
 }
 void main(string[] args)
 {
 int[] a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ];
 do_something(stride(a,3));
 }


 I get:
 moo.d(9): Error: function moo.do_something (int[] values) is not
 callable using argument types (Result)
 moo.d(9): Error: cannot implicitly convert expression (stride(a,3LU))
 of type Result to int[]

 Two options, first, you can change do_something to accept a range
 (depending on what the real implementation of do_something is, you might
 need to require a random-access range, but that dummy implementation
 could accept any input range, just return x.front):

 int do_something(R)(R values) if (isInputRange!R && is(ElementType!R :
 int))
 {
 return values.front; // maybe need random access in real code?
 }

 Second option, convert range to an array. This incurs a memory
 allocation to create the array:

 import std.array;

 ...
 void main(...)
 {
 ...
 do_something(array(stride(a, 3)));
 }

 doc for std.array.array:
 http://www.d-programming-language.org/phobos/std_array.html#array

 -Steve

Both of those solutions worked, thanks :)

Aug 09 2011

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digitalmars.D.learn - We have slices, do we have Strides?