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

[Arunkumar Srinivasan]

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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