[datatable-help] changing data.table by-without-by syntax to require a "by"

[Matthew Dowle]

That sentence on that linked webpage seems incorect English, since
table is a noun not a verb. Should "table" be "join" perhaps? 

Anyway,
by-without-by is often used with join inherited scope (JIS). For
example, translating their example : 

1> X = data.table(a=1:3,b=1:15,
key="a")
1> X
 a b
 1: 1 1
 2: 1 4
 3: 1 7
 4: 1 10
 5: 1 13
 6: 2 2
 7:
2 5
 8: 2 8
 9: 2 11
10: 2 14
11: 3 3
12: 3 6
13: 3 9
14: 3 12
15: 3
15
1> Y = data.table(a=c(1,2), top=c(3,4))
1> Y
 a top
1: 1 3
2: 2 4
1>
X[Y, head(.SD,i.top)]
 a b
1: 1 1
2: 1 4
3: 1 7
4: 2 2
5: 2 5
6: 2 8
7:
2 11
1> 

If there was no by-without-by (analogous to CROSS BY), then
how would that be done?

On 24.04.2013 22:22, Eduard Antonyan wrote: 

>
By that you mean current behavior? You'd get current behavior by
explicitly specifying the appropriate "by" (i.e. "by" equal to the key).

> Btw, I'm trying to understand SQL CROSS APPLY vs JOIN using
http://explainextended.com/2009/07/16/inner-join-vs-cross-apply/ [8],
and I can't figure out how by-without-by (or with by-with-by for that
matter:) ) helps with e.g. the first example there: 
> "We table table1
and table2. table1 has a column called rowcount. 
> 
> For each row from
table1 we need to select first rowcount rows from table2, ordered by
table2.id [9]" 
> 
> On Wed, Apr 24, 2013 at 4:01 PM, Matthew Dowle
<mdowle at mdowle.plus.com [10]> wrote:
> 
>> But then what would be
analogous to CROSS APPLY in SQL?
>> 
>> > I'd agree with Eduard,
although it's probably too late to change behavior
>> > now. Maybe for
data.table.2? Eduard's proposal seems more closely
>> > aligned with SQL
behavior as well (SELECT/JOIN, then GROUP, but only if
>> >
requested).
>> >
>> > S.
>> >
>> >> Date: Mon, 22 Apr 2013 08:17:59
-0700 >> From: eduard.antonyan at gmail.com [1]
>> >> To:
datatable-help at lists.r-forge.r-project.org [2]
>> 
>>>> Subject: Re:
[datatable-help] changing data.table by-without-by
>> >> syntax to
require a "by"
>> >>
>> >> I think you're missing the point Michael.
Just because it's possible to
>> >> do it
>> >> the way it's done now,
doesn't mean that's the best way, as I've tried
>> >> to
>> >> argue in
the OP. I don't think you've addressed the issue of unnecessary
>> >>
complexity pointed out in OP.
>> >>
>> >>
>> >>
>> >> --
>> >> View this
message in context:
>> >>
http://r.789695.n4.nabble.com/changing-data-table-by-without-by-syntax-to-require-a-by-tp4664770p4664990.html
[3]
>> >> Sent from the datatable-help mailing list archive at
Nabble.com.
>> >> _______________________________________________
>> >>
datatable-help mailing list >>
datatable-help at lists.r-forge.r-project.org [4]
>> 
>>>>
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
[5]
>> > _______________________________________________
>> >
datatable-help mailing list > datatable-help at lists.r-forge.r-project.org
[6]
>> >
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
[7]

 

Links:
------
[1] mailto:eduard.antonyan at gmail.com
[2]
mailto:datatable-help at lists.r-forge.r-project.org
[3]
http://r.789695.n4.nabble.com/changing-data-table-by-without-by-syntax-to-require-a-by-tp4664770p4664990.html
[4]
mailto:datatable-help at lists.r-forge.r-project.org
[5]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
[6]
mailto:datatable-help at lists.r-forge.r-project.org
[7]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
[8]
http://explainextended.com/2009/07/16/inner-join-vs-cross-apply/
[9]
http://table2.id
[10] mailto:mdowle at mdowle.plus.com
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