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[ATL] Why returning a sequence of a sequence ? [message #57021]

Thu, 09 August 2007 14:47

Guillaume Gauffre

Messages: 65
Registered: July 2009

Member

Hi,

considering these 3 operations on the Set 'totargets' :

totargets.debug('relFromS');
totargets->collect(e|e.target).debug('AOut');
totargets->collect(e|e.target)->collect(e|e.relationShipSources).debug('relToR');

the two first operations print well a sequence for each, but the third
prints a sequence of a sequence 'Sequence {Sequence {IN!<unnamed>,
IN!<unnamed>, IN!<unnamed>}}'. Why this behaviour ?
I must use the operation flatten() to finally get my sequence !

Thanks

Guillaume

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Re: [ATL] Why returning a sequence of a sequence ? [message #57074 is a reply to message #57021]

Thu, 09 August 2007 15:51

Frédéric Jouault

Messages: 572
Registered: July 2009

Senior Member

Hi,

> considering these 3 operations on the Set 'totargets' :
>
> totargets.debug('relFromS');
> totargets->collect(e|e.target).debug('AOut');
>
totargets->collect(e|e.target)->collect(e|e.relationShipSources).debug('relToR');

>
>
> the two first operations print well a sequence for each, but the third
> prints a sequence of a sequence 'Sequence {Sequence {IN!<unnamed>,
> IN!<unnamed>, IN!<unnamed>}}'. Why this behaviour ?

Sometimes you want to get a Sequence of Sequence.

> I must use the operation flatten() to finally get my sequence !

Yes.

Of course, we could have the "collectNested" iterator that would return
a Sequence of Sequence. The collect iterator would then consist of
"collectNested" followed by a call to "flatten".

However, switching for this alternate behavior would break some existing
transformations relying on the way it currently works.

Regards,

Frédéric Jouault

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Re: [ATL] Why returning a sequence of a sequence ? [message #57100 is a reply to message #57074]

Thu, 09 August 2007 15:58

Guillaume Gauffre

Messages: 65
Registered: July 2009

Member

Ok, fine !

Thank you for your rapid response

Guillaume

Frédéric Jouault a écrit :
> Hi,
>
> > considering these 3 operations on the Set 'totargets' :
> >
> > totargets.debug('relFromS');
> > totargets->collect(e|e.target).debug('AOut');
> >
> totargets->collect(e|e.target)->collect(e|e.relationShipSources).debug('relToR');
>
> >
> >
> > the two first operations print well a sequence for each, but the third
> > prints a sequence of a sequence 'Sequence {Sequence {IN!<unnamed>,
> > IN!<unnamed>, IN!<unnamed>}}'. Why this behaviour ?
>
> Sometimes you want to get a Sequence of Sequence.
>
>
> > I must use the operation flatten() to finally get my sequence !
>
> Yes.
>
>
> Of course, we could have the "collectNested" iterator that would return
> a Sequence of Sequence. The collect iterator would then consist of
> "collectNested" followed by a call to "flatten".
>
> However, switching for this alternate behavior would break some existing
> transformations relying on the way it currently works.
>
>
> Regards,
>
> Frédéric Jouault

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