A character vector of variables to join by.
If NULL
, the default, *_join()
will perform a natural join, using all
variables in common across x
and y
. A message lists the variables so that you
can check they're correct; suppress the message by supplying by
explicitly.
To join by different variables on x
and y
, use a named vector.
For example, by = c("a" = "b")
will match x$a
to y$b
.
To join by multiple variables, use a vector with length > 1.
For example, by = c("a", "b")
will match x$a
to y$a
and x$b
to
y$b
. Use a named vector to match different variables in x
and y
.
For example, by = c("a" = "b", "c" = "d")
will match x$a
to y$b
and
x$c
to y$d
.
To perform a cross-join, generating all combinations of x
and y
,
use by = character()
.