Each item of l
can be a data.table
, data.frame
or list
, including NULL
(skipped) or an empty object (0 rows). rbindlist
is most useful when there are a variable number of (potentially many) objects to stack, such as returned by lapply(fileNames, fread)
. rbind
however is most useful to stack two or three objects which you know in advance. …
should contain at least one data.table
for rbind(…)
to call the fast method and return a data.table
, whereas rbindlist(l)
always returns a data.table
even when stacking a plain list
with a data.frame
, for example.
In versions <= v1.9.2
, each item for rbindlist
should have the same number of columns as the first non empty item. rbind.data.table
gained a fill
argument to fill missing columns with NA
in v1.9.2
, which allowed for rbind(…)
binding unequal number of columns.
In version > v1.9.2
, these functionalities were extended to rbindlist
(and written entirely in C for speed). rbindlist
has use.names
argument, which is set to FALSE
by default for backwards compatibility. It also contains fill
argument as well and can bind unequal columns when set to TRUE
.
With these changes, the only difference between rbind(…)
and rbindlist(l)
is their default argument use.names
.
If column i
of input items do not all have the same type; e.g, a data.table
may be bound with a list
or a column is factor
while others are character
types, they are coerced to the highest type (SEXPTYPE).
Note that any additional attributes that might exist on individual items of the input list would not be preserved in the result.