join: Join two unitted data.frames
In appling/unitted: Track Units as you Manipulate Data

Uses the corresponding dplyr join functions.

## S3 method for class 'unitted_data.frame'
inner_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_data.frame'
left_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_data.frame'
right_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_data.frame'
full_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_data.frame'
semi_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_data.frame'
anti_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_tbl_df'
inner_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_tbl_df'
left_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_tbl_df'
right_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_tbl_df'
full_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_tbl_df'
semi_join(x, y, by = NULL, copy = FALSE, ...)

## S3 method for class 'unitted_tbl_df'
anti_join(x, y, by = NULL, copy = FALSE, ...)

`x`	left-hand-side table to join
`y`	right-hand-side table to join
`by`	a character vector of variables to join by. If `NULL`, the default, `*_join()` will do a natural join, using all variables with common names across the two tables. A message lists the variables so that you can check they're right (to suppress the message, simply explicitly list the variables that you want to join). 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`.
`copy`	If `x` and `y` are not from the same data source, and `copy` is `TRUE`, then `y` will be copied into the same src as `x`. This allows you to join tables across srcs, but it is a potentially expensive operation so you must opt into it.
`...`	other parameters passed onto methods