The constructor and generics described here define a class that helps separating dplyr's user interface from the actual underlying operations. In the longer term, this will help packages that implement the dplyr interface (such as dbplyr, dtplyr, arrow and similar) to focus on the core details of their functionality, rather than on the intricacies of dplyr's user interface.
new_relational() constructs an object of class "relational".
Users are encouraged to provide the class argument.
The typical use case will be to create a wrapper function.
rel_to_df() extracts a data frame representation from a relational object,
to be used by dplyr::collect().
rel_filter() keeps rows that match a predicate,
to be used by dplyr::filter().
rel_project() selects columns or creates new columns,
to be used by dplyr::select(), dplyr::rename(),
dplyr::mutate(), dplyr::relocate(), and others.
rel_aggregate() combines several rows into one,
to be used by dplyr::summarize().
rel_order() reorders rows by columns or expressions,
to be used by dplyr::arrange().
rel_join() joins or merges two tables,
to be used by dplyr::left_join(), dplyr::right_join(),
dplyr::inner_join(), dplyr::full_join(), dplyr::cross_join(),
dplyr::semi_join(), and dplyr::anti_join().
rel_limit() limits the number of rows in a table,
to be used by utils::head().
rel_distinct() only keeps the distinct rows in a table,
to be used by dplyr::distinct().
rel_set_intersect() returns rows present in both tables,
to be used by intersect().
rel_set_diff() returns rows present in any of both tables,
to be used by setdiff().
rel_set_symdiff() returns rows present in any of both tables,
to be used by dplyr::symdiff().
rel_union_all() returns rows present in any of both tables,
to be used by dplyr::union_all().
rel_explain() prints an explanation of the plan
executed by the relational object.
rel_alias() returns the alias name for a relational object.
rel_set_alias() sets the alias name for a relational object.
rel_names() returns the column names as character vector,
to be used by colnames().
Usage
new_relational(..., class = NULL)
rel_to_df(rel, ...)
rel_filter(rel, exprs, ...)
rel_project(rel, exprs, ...)
rel_aggregate(rel, groups, aggregates, ...)
rel_order(rel, orders, ...)
rel_join(
left,
right,
conds,
join = c("inner", "left", "right", "outer", "cross", "semi", "anti"),
join_ref_type = c("regular", "natural", "cross", "positional", "asof"),
...
)
rel_limit(rel, n, ...)
rel_distinct(rel, ...)
rel_set_intersect(rel_a, rel_b, ...)
rel_set_diff(rel_a, rel_b, ...)
rel_set_symdiff(rel_a, rel_b, ...)
rel_union_all(rel_a, rel_b, ...)
rel_explain(rel, ...)
rel_alias(rel, ...)
rel_set_alias(rel, alias, ...)
rel_names(rel, ...)Arguments
- ...
Reserved for future extensions, must be empty.
- class
Classes added in front of the
"relational"base class.- rel, rel_a, rel_b, left, right
A relational object.
- exprs
A list of expr objects to filter by.
- groups
A list of expressions to group by.
- aggregates
A list of expressions with aggregates to compute.
- orders
A list of expressions to order by.
- conds
A list of expressions to use for the join.
- join
The type of join.
- join_ref_type
The ref type of join.
- n
The number of rows.
- alias
the new alias
Value
new_relational()returns a new relational object.rel_to_df()returns a data frame.rel_names()returns a character vector.All other generics return a modified relational object.
Examples
new_dfrel <- function(x) {
stopifnot(is.data.frame(x))
new_relational(list(x), class = "dfrel")
}
mtcars_rel <- new_dfrel(mtcars[1:5, 1:4])
rel_to_df.dfrel <- function(rel, ...) {
unclass(rel)[[1]]
}
rel_to_df(mtcars_rel)
#> mpg cyl disp hp
#> Mazda RX4 21.0 6 160 110
#> Mazda RX4 Wag 21.0 6 160 110
#> Datsun 710 22.8 4 108 93
#> Hornet 4 Drive 21.4 6 258 110
#> Hornet Sportabout 18.7 8 360 175
rel_filter.dfrel <- function(rel, exprs, ...) {
df <- unclass(rel)[[1]]
# A real implementation would evaluate the predicates defined
# by the exprs argument
new_dfrel(df[seq_len(min(3, nrow(df))), ])
}
rel_filter(
mtcars_rel,
list(
relexpr_function(
"gt",
list(relexpr_reference("cyl"), relexpr_constant("6"))
)
)
)
#> [[1]]
#> mpg cyl disp hp
#> Mazda RX4 21.0 6 160 110
#> Mazda RX4 Wag 21.0 6 160 110
#> Datsun 710 22.8 4 108 93
#>
#> attr(,"class")
#> [1] "dfrel" "relational"
rel_project.dfrel <- function(rel, exprs, ...) {
df <- unclass(rel)[[1]]
# A real implementation would evaluate the expressions defined
# by the exprs argument
new_dfrel(df[seq_len(min(3, ncol(df)))])
}
rel_project(
mtcars_rel,
list(relexpr_reference("cyl"), relexpr_reference("disp"))
)
#> [[1]]
#> mpg cyl disp
#> Mazda RX4 21.0 6 160
#> Mazda RX4 Wag 21.0 6 160
#> Datsun 710 22.8 4 108
#> Hornet 4 Drive 21.4 6 258
#> Hornet Sportabout 18.7 8 360
#>
#> attr(,"class")
#> [1] "dfrel" "relational"
rel_order.dfrel <- function(rel, exprs, ...) {
df <- unclass(rel)[[1]]
# A real implementation would evaluate the expressions defined
# by the exprs argument
new_dfrel(df[order(df[[1]]), ])
}
rel_order(
mtcars_rel,
list(relexpr_reference("mpg"))
)
#> [[1]]
#> mpg cyl disp hp
#> Hornet Sportabout 18.7 8 360 175
#> Mazda RX4 21.0 6 160 110
#> Mazda RX4 Wag 21.0 6 160 110
#> Hornet 4 Drive 21.4 6 258 110
#> Datsun 710 22.8 4 108 93
#>
#> attr(,"class")
#> [1] "dfrel" "relational"
rel_join.dfrel <- function(left, right, conds, join, ...) {
left_df <- unclass(left)[[1]]
right_df <- unclass(right)[[1]]
# A real implementation would evaluate the expressions
# defined by the conds argument,
# use different join types based on the join argument,
# and implement the join itself instead of relaying to left_join().
new_dfrel(dplyr::left_join(left_df, right_df))
}
rel_join(new_dfrel(data.frame(mpg = 21)), mtcars_rel)
#> Joining with `by = join_by(mpg)`
#> [[1]]
#> mpg cyl disp hp
#> 1 21 6 160 110
#> 2 21 6 160 110
#>
#> attr(,"class")
#> [1] "dfrel" "relational"
rel_limit.dfrel <- function(rel, n, ...) {
df <- unclass(rel)[[1]]
new_dfrel(df[seq_len(n), ])
}
rel_limit(mtcars_rel, 3)
#> [[1]]
#> mpg cyl disp hp
#> Mazda RX4 21.0 6 160 110
#> Mazda RX4 Wag 21.0 6 160 110
#> Datsun 710 22.8 4 108 93
#>
#> attr(,"class")
#> [1] "dfrel" "relational"
rel_distinct.dfrel <- function(rel, ...) {
df <- unclass(rel)[[1]]
new_dfrel(df[!duplicated(df), ])
}
rel_distinct(new_dfrel(mtcars[1:3, 1:4]))
#> [[1]]
#> mpg cyl disp hp
#> Mazda RX4 21.0 6 160 110
#> Datsun 710 22.8 4 108 93
#>
#> attr(,"class")
#> [1] "dfrel" "relational"
rel_names.dfrel <- function(rel, ...) {
df <- unclass(rel)[[1]]
names(df)
}
rel_names(mtcars_rel)
#> [1] "mpg" "cyl" "disp" "hp"