[datatable-help] probably undesirable function of `rbindlist`

[Ricardo Saporta]

Arun,

Im pretty sure `rbindlist` identifies column class based on the first
argument.

compare
  rbindlist(list(DT2, DT1))
  rbindlist(list(DT1, DT2))


I agree with you though that a more ideal behavior would be one that mimics
`c( )`


-Rick


On Sat, Jul 27, 2013 at 3:07 PM, Arunkumar Srinivasan <aragorn168b at gmail.com
> wrote:

>  Hi all,
>
> Here's a behaviour of `rbindlist` that I came across that I think is
> undesirable. If the columns to be "rbind" are of type "integer" and
> "numeric", then, the class "integer" is retained which results in different
> results than intended.
>
> require(data.table)
> DT1 <- data.table(x = 1:5, y = 1:5)
>    x y
> 1: 1 1
> 2: 2 2
> 3: 3 3
> 4: 4 4
> 5: 5 5
>
> DT2 <- data.table(x = 6:10, y = 1:5/10)
>     x   y
> 1:  6 0.1
> 2:  7 0.2
> 3:  8 0.3
> 4:  9 0.4
> 5: 10 0.5
>
> sapply(DT1, class)
>         x         y
> "integer" "integer"
>
> sapply(DT2, class)
>         x         y
> "integer" "numeric"
>
> rbindlist(list(DT1, DT2))
>      x y
>  1:  1 1
>  2:  2 2
>  3:  3 3
>  4:  4 4
>  5:  5 5
>  6:  6 0 <~~~~ from here, the result should be 0.1 to 0.5 for the next 5
> rows or y.
>  7:  7 0
>  8:  8 0
>  9:  9 0
> 10: 10 0
>
> Is this behaviour unexpected or we've to manually take care of this? Seems
> more proper to be taken care of internally to me though.
>
> Best,
> Arun.
>
>
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