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

reply 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
next sibling parent reply "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
parent reply 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
next sibling parent "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
prev sibling next sibling parent 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
prev sibling parent reply 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
parent 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
prev sibling next sibling parent "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
prev sibling next sibling parent "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
prev sibling parent "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