[datatable-help] POSIXct as data.table key

[Matthew Dowle]

Welcome.

No time right now to test, so just quick reply...

This is the correct form (that you correctly tried) :

d[list(n+days(1)),]

or you can use these (all identical) :

d[list(n+days(1))]   # comma is optional
d[J(n+days(1))]
d[.(n+days(1))]

I don't know libridate, but I guess the reason for :

> Error in `[.data.table`(d, list(n + days(1)), ) :
>   typeof x.t (integer) != typeof i.V1 (double)

might be, try

d[J(n+days(1L))]

instead of

d[J(n+days(1))]

> I can query using a boolean, but I assume this is skipping the index on
> 't'?

Yes, exactly.


> Hi,
>
> I see at
> https://r-forge.r-project.org/tracker/index.php?func=detail&aid=1482&group_id=240&atid=978
> that POSIXct values are supported as key.  But I'm unsure how to
> efficiently query them.  Here are my attempts:
>
>> library(lubridate)
>> n <- now()
>> d <- data.table(t=n+days(1:10), val=runif(10), key='t')
>> d[n+days(1)]
> Error in `[.data.table`(d, n + days(1)) :
>   i has not evaluated to logical, integer or double
>> d[n+days(1),]
> Error in `[.data.table`(d, n + days(1), ) :
>   i has not evaluated to logical, integer or double
>> d[list(n+days(1)),]
> Error in `[.data.table`(d, list(n + days(1)), ) :
>   typeof x.t (integer) != typeof i.V1 (double)
>
>
> I can query using a boolean, but I assume this is skipping the index on
> 't'?
>
>> d[t==n+days(1),]
>                        t       val
> [1,] 2012-09-22 21:06:52 0.2550606
>
>
> Thanks.
>
>
> --
> Ken Williams, Senior Research Scientist
> WindLogics
> http://windlogics.com
>
>
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