code review 7376058: sort: add an example showing sorting struct by differen...

sort: add an example showing sorting struct by different keys

[r, 2013-02-26 23:25:39]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[r, 2013-02-26 23:40:43]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

Please take another look.

[dsymonds, 2013-02-26 23:45:13]

https://codereview.appspot.com/7376058/diff/3001/src/pkg/sort/example_keys_te...
File src/pkg/sort/example_keys_test.go (right):

https://codereview.appspot.com/7376058/diff/3001/src/pkg/sort/example_keys_te...
src/pkg/sort/example_keys_test.go:49: s.planets = planets
splitting this setup seems a little odd, and means you can't use Sort
concurrently, nor even call String before sorting. The simplest solution would
be two types (a func and a func+slice).

[r, 2013-02-26 23:47:38]

I don't understand your proposal.

-rob

[r, 2013-02-26 23:50:56]

Hello golang-dev@googlegroups.com, dsymonds@golang.org (cc:
golang-dev@googlegroups.com),

Please take another look.

[dsymonds, 2013-02-26 23:51:34]

On Wed, Feb 27, 2013 at 10:47 AM, Rob Pike <r@golang.org> wrote:

> I don't understand your proposal.

Have
  type planetComparer func(p1, p2 *Planet) bool
which is returned by the By function. It has a Sort method that takes
a []Planet as you currently have it, but then uses a second type,
something like
  type planetSorter struct {
    less func(p1, p2 *Planet) bool
    s []Planet
  }
on which the Len/Less/Swap methods are hung. The Sort method creates a
new instance of that struct each call, and passes it to sort.Sort to
do the work.

[r, 2013-02-26 23:52:23]

That's a lot of boilerplate. I was trying to write something small and
pretty. Let me think about it some more.

-rob

[r, 2013-02-27 00:45:42]

Hello golang-dev@googlegroups.com, dsymonds@golang.org (cc:
golang-dev@googlegroups.com),

Please take another look.

[r, 2013-02-27 00:46:43]

I think I semi-independently came up with your approach, and it's
slightly more magical but a good example.
Plus methods on functions are always fun.

-rob

[dsymonds, 2013-02-27 01:02:19]

LGTM

that's nicer.

[r, 2013-02-27 01:17:53]

*** Submitted as https://code.google.com/p/go/source/detail?r=2bf8d07c14c1 ***

sort: add an example showing sorting struct by different keys

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/7376058

[adg, 2013-02-27 02:05:20]

https://codereview.appspot.com/7376058/diff/14001/src/pkg/sort/example_keys_t...
File src/pkg/sort/example_keys_test.go (right):

https://codereview.appspot.com/7376058/diff/14001/src/pkg/sort/example_keys_t...
src/pkg/sort/example_keys_test.go:63: // ExampleSortKeys demonstrates a
technique for sorting a struct type using programmable sort criteria.
Example_SortKeys ?

https://codereview.appspot.com/7376058/diff/14001/src/pkg/sort/example_keys_t...
src/pkg/sort/example_keys_test.go:64: func Example_sortKeys() {
capital S?

[r, 2013-02-27 02:12:32]

According to package testing, it must be lower case or godoc will
insist it be an exported identifier in the package.

-rob

[mtj1, 2013-02-27 02:15:28]

Might there be a clever way to chain these for multiple keys? (by X and
then by Y)

On Tue, Feb 26, 2013 at 9:05 PM, <adg@golang.org> wrote:

>
> https://codereview.appspot.**com/7376058/diff/14001/src/**
>
pkg/sort/example_keys_test.go<https://codereview.appspot.com/7376058/diff/14001/src/pkg/sort/example_keys_test.go>
> File src/pkg/sort/example_keys_**test.go (right):
>
> https://codereview.appspot.**com/7376058/diff/14001/src/**
>
pkg/sort/example_keys_test.go#**newcode63<https://codereview.appspot.com/7376058/diff/14001/src/pkg/sort/example_keys_test.go#newcode63>
> src/pkg/sort/example_keys_**test.go:63: // ExampleSortKeys demonstrates a
> technique for sorting a struct type using programmable sort criteria.
> Example_SortKeys ?
>
> https://codereview.appspot.**com/7376058/diff/14001/src/**
>
pkg/sort/example_keys_test.go#**newcode64<https://codereview.appspot.com/7376058/diff/14001/src/pkg/sort/example_keys_test.go#newcode64>
> src/pkg/sort/example_keys_**test.go:64: func Example_sortKeys() {
> capital S?
>
>
>
https://codereview.appspot.**com/7376058/<https://codereview.appspot.com/7376...
>
> --
>
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>


-- 
Michael T. Jones | Chief Technology Advocate  | mtj@google.com |  +1
650-335-5765

[adg, 2013-02-27 02:15:49]

I forgot about that.


On 27 February 2013 13:12, Rob Pike <r@golang.org> wrote:

> According to package testing, it must be lower case or godoc will
> insist it be an exported identifier in the package.
>
> -rob
>

[r, 2013-02-27 04:53:18]

On Tue, Feb 26, 2013 at 6:14 PM, Michael Jones <mtj@google.com> wrote:
> Might there be a clever way to chain these for multiple keys? (by X and then
> by Y)

I'm sure there is.

-rob

[adg, 2013-02-27 04:59:48]

On 27 February 2013 13:14, Michael Jones <mtj@google.com> wrote:

> Might there be a clever way to chain these for multiple keys? (by X and
> then by Y)


Sure:

nameAndDistance := func(p1, p2 *Planet) bool {
  if p1.name == p2.name {
    return distance(p1, p2)
  }
  return name(p1, p2)
}

[mtj1, 2013-02-27 05:04:02]

Ooh, so that should be in the example. ;-)

On Tue, Feb 26, 2013 at 11:59 PM, Andrew Gerrand <adg@golang.org> wrote:

>
> On 27 February 2013 13:14, Michael Jones <mtj@google.com> wrote:
>
>> Might there be a clever way to chain these for multiple keys? (by X and
>> then by Y)
>
>
> Sure:
>
> nameAndDistance := func(p1, p2 *Planet) bool {
>   if p1.name == p2.name {
>     return distance(p1, p2)
>   }
>   return name(p1, p2)
> }
>
>


-- 
Michael T. Jones | Chief Technology Advocate  | mtj@google.com |  +1
650-335-5765

[adg, 2013-02-27 05:12:58]

The dataset doesn't really lend itself to being sorted in multiple
dimensions because none of rows have common values in any field.


On 27 February 2013 16:03, Michael Jones <mtj@google.com> wrote:

> Ooh, so that should be in the example. ;-)
>
>
> On Tue, Feb 26, 2013 at 11:59 PM, Andrew Gerrand <adg@golang.org> wrote:
>
>>
>> On 27 February 2013 13:14, Michael Jones <mtj@google.com> wrote:
>>
>>> Might there be a clever way to chain these for multiple keys? (by X and
>>> then by Y)
>>
>>
>> Sure:
>>
>> nameAndDistance := func(p1, p2 *Planet) bool {
>>   if p1.name == p2.name {
>>     return distance(p1, p2)
>>   }
>>   return name(p1, p2)
>> }
>>
>>
>
>
> --
> Michael T. Jones | Chief Technology Advocate  | mtj@google.com |  +1
> 650-335-5765
>

[r, 2013-02-27 07:22:54]

I'd use a slice of functions, and call the next element of the slice
only if the first function claims equality. An exercise for the reader
to construct.

-rob

[adg, 2013-02-27 21:29:43]

On 27 February 2013 18:22, Rob Pike <r@golang.org> wrote:

> the first function claims equality.


How does that work? !fn(a, b) && !fn(b, a) ?

[r, 2013-02-27 21:31:32]

*a == *b sounds fine to me in this case, but that would work too.

-rob