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#' Subset, rename, and reorder columns using their names
#'
#' @description
#' These are methods for the dplyr [select()], [rename()], and [relocate()]
#' generics. They generate the `SELECT` clause of the SQL query.
#'
#' These functions do not support predicate functions, i.e. you can
#' not use `where(is.numeric)` to select all numeric variables.
#'
#' @inheritParams arrange.tbl_lazy
#' @inheritParams dplyr::select
#' @export
#' @importFrom dplyr select
#' @examples
#' library(dplyr, warn.conflicts = FALSE)
#'
#' db <- memdb_frame(x = 1, y = 2, z = 3)
#' db %>% select(-y) %>% show_query()
#' db %>% relocate(z) %>% show_query()
#' db %>% rename(first = x, last = z) %>% show_query()
select.tbl_lazy <- function(.data, ...) {
loc <- tidyselect::eval_select(expr(c(...)), .data)
loc <- ensure_group_vars(loc, .data, notify = TRUE)
new_vars <- set_names(colnames(.data)[loc], names(loc))
.data$lazy_query <- add_select(.data, new_vars)
.data
}
ensure_group_vars <- function(loc, data, notify = TRUE) {
group_loc <- match(group_vars(data), colnames(data))
missing <- setdiff(group_loc, loc)
if (length(missing) > 0) {
vars <- colnames(data)[missing]
if (notify) {
cli::cli_inform("Adding missing grouping variables: {.var {vars}}")
}
loc <- c(set_names(missing, vars), loc)
}
loc
}
#' @rdname select.tbl_lazy
#' @importFrom dplyr rename
#' @export
rename.tbl_lazy <- function(.data, ...) {
loc <- tidyselect::eval_rename(expr(c(...)), .data)
new_vars <- set_names(colnames(.data), colnames(.data))
names(new_vars)[loc] <- names(loc)
.data$lazy_query <- add_select(.data, new_vars)
.data
}
#' @rdname select.tbl_lazy
#' @importFrom dplyr rename_with
#' @importFrom tidyselect everything
#' @inheritParams dplyr::rename_with
#' @export
rename_with.tbl_lazy <- function(.data, .fn, .cols = everything(), ...) {
.fn <- as_function(.fn)
cols <- tidyselect::eval_select(enquo(.cols), .data)
new_vars <- set_names(op_vars(.data))
names(new_vars)[cols] <- .fn(new_vars[cols], ...)
.data$lazy_query <- add_select(.data, new_vars)
.data
}
#' @rdname select.tbl_lazy
#' @importFrom dplyr relocate
#' @inheritParams dplyr::relocate
#' @export
relocate.tbl_lazy <- function(.data, ..., .before = NULL, .after = NULL) {
loc <- tidyselect::eval_relocate(
expr(c(...)),
data = .data,
before = enquo(.before),
after = enquo(.after),
before_arg = ".before",
after_arg = ".after"
)
dplyr::select(.data, !!!loc)
}
#' Simulate variables to use in tidyselect
#'
#' @param x A lazy table
#' @param drop_groups Should groups be dropped?
#'
#' @return A 0 row tibble with the same columns names, and, if possible, types, as `x`.
#'
#' @export
#' @keywords internal
simulate_vars <- function (x, drop_groups = FALSE) {
# keep this for now as this might be used by other packages
UseMethod("simulate_vars")
}
#' @export
simulate_vars.tbl_lazy <- function(x, drop_groups = FALSE) {
if (drop_groups) {
vars <- setdiff(op_vars(x), op_grps(x))
} else {
vars <- op_vars(x)
}
as_tibble(rep_named(vars, list(logical())), .name_repair = "minimal")
}
#' @rdname simulate_vars
#' @export
simulate_vars_is_typed <- function(x) UseMethod("simulate_vars_is_typed")
#' @export
simulate_vars_is_typed.tbl_lazy <- function(x) FALSE
# op_select ---------------------------------------------------------------
add_select <- function(.data, vars) {
lazy_query <- .data$lazy_query
stopifnot(is.character(vars))
if (is_identity(syms(vars), names(vars), op_vars(.data))) {
return(lazy_query)
}
lazy_query <- rename_groups(lazy_query, vars)
is_join <- inherits(lazy_query, "lazy_multi_join_query") || inherits(lazy_query, "lazy_semi_join_query")
is_select <- inherits(lazy_query, "lazy_select_query")
if (is_join || is_select) {
names_prev <- op_vars(lazy_query)
idx <- vctrs::vec_match(vars, names_prev)
if (is_join) {
lazy_query$vars <- vctrs::vec_slice(lazy_query$vars, idx)
lazy_query$vars$name <- names(vars)
} else {
lazy_query$select <- vctrs::vec_slice(lazy_query$select, idx)
lazy_query$select$name <- names(vars)
}
return(lazy_query)
}
lazy_select_query(
x = lazy_query,
select_operation = "select",
select = syms(vars)
)
}
rename_groups <- function(lazy_query, vars) {
old2new <- set_names(names(vars), vars)
grps <- op_grps(lazy_query)
renamed <- grps %in% names(old2new)
grps[renamed] <- old2new[grps[renamed]]
lazy_query$group_vars <- grps
lazy_query
}
is_projection <- function(exprs) {
purrr::every(exprs, is_symbol)
}
is_pure_projection <- function(exprs, names) {
if (!is_projection(exprs)) {
return(FALSE)
}
expr_vars <- purrr::map_chr(unname(exprs), as_string)
identical(expr_vars, names)
}
is_identity <- function(exprs, names, names_prev) {
if (!is_pure_projection(exprs, names)) {
return(FALSE)
}
identical(names, names_prev)
}
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