[datatable-help] aggregating data

[David Bellot]

actually I found the issue. That was not related to data.table but because
I'm comparing float values, it breaks all the time if I do not round() my
values before. Basically I have values like 0,1, 1.5, 0.5 etc...
I know it's bad to do that but I'm not the boss in this project ;-)

Just in case other users are reading my email, I can only advise to read
that again and again:
http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

Best,
David


On Tue, Apr 9, 2013 at 11:39 AM, Matthew Dowle <mdowle at mdowle.plus.com>wrote:

> **
>
>
>
> That's odd.  Please provide result of sessionInfo() and str(DT).
>
> Matthew
>
>
>
> On 09.04.2013 11:32, David Bellot wrote:
>
>  Hi,
>
> I have a data.table DT with one of the column named x and I other names,
> let's say, a1, a2, ... aN. The key of this data.table is made of a1...aN.
>
> Later on, I aggregate my DT with x like this:
> agg = DT[ , list(m=mean(y), c=length(y)), by = c("x") ]
>
> The problem is that "x" has 331 unique values as found by
> length(unique(DT$x)) but my result "agg" only has 119 rows. I tried by
> changing the key to "x" alone but the problem persists. My DT table has a
> few millions rows by the way.
>
> I'm sure I'm missing something totally obvious :-( !!!!
>
> Any idea ?
> Best,
> David
>
>
>
>
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