[jira] [Commented] (TINKERPOP-2520) Add the ability to reverse the stream or a collection

["Stephen Mallette (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TINKERPOP-2520?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17281883#comment-17281883 ] 

Stephen Mallette commented on TINKERPOP-2520:
---------------------------------------------

Been thinking about this one a bit. I think we should simply disallow things like:

{code}
g.V().order().by('name').by(reverse)
g.V().order().by(reverse).by('name')
g.V().order().by(reverse).by(shuffle)
{code}

You can simply:

{code}
g.V().order().by(reverse)
{code}

We have similar rules around {{shuffle}} already but they don't explicitly result in error - the {{shuffle}} steps in between comparators are just removed and the mode of the order only goes to {{shuffle}} if that is the last {{Comparator}}.

This would not prevent:

{code}
// g.V().order().by('name',desc)
g.V().
  order().by('name').
  order().by(reverse)
{code}

I think that rather that doing magic with {{shuffle}} (and trying to do the same with {{reverse}}) perhaps we just require Gremlin to be formed where multiple {{Comparator}} instances can't be present where {{shuffle}} and {{reverse}} are in play. 

> Add the ability to reverse the stream or a collection
> -----------------------------------------------------
>
>                 Key: TINKERPOP-2520
>                 URL: https://issues.apache.org/jira/browse/TINKERPOP-2520
>             Project: TinkerPop
>          Issue Type: Improvement
>          Components: process
>    Affects Versions: 3.4.10
>            Reporter: Kelvin R. Lawrence
>            Priority: Minor
>
> I had a Gremlin user ask me yesterday if there was a way to have the results of a `path` step be reversed. Today you cannot do that using `from` and `to` steps as the `from` label must appear before the `to` label in a path. In thinking about this, perhaps adding a `reverse` option to order (on top of `asc`,`desc` and `shuffle`) would be a nice addition to Gremlin. So you could write something like:
> {code:java}
> g.V().out().out().path().order(local).by(reverse){code}
> For this specific user they were union-ing a set of paths in different directions and wanted to normalize them to all be in the same direction when presented as results.



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