paleolimbot commented on code in PR #35543:
URL: https://github.com/apache/arrow/pull/35543#discussion_r1235299471
##########
r/R/schema.R:
##########
@@ -244,10 +230,59 @@ print_schema_fields <- function(s) {
paste(map_chr(s$fields, ~ .$ToString()), collapse = "\n")
}
-#' @param ... [fields][field] or field name/[data type][data-type] pairs
+#' Schemas
+#'
+#' Create a schema or extract one from an object.
+#'
+#' @seealso [Schema] for detailed documentation of the Schema R6 object
+#' @param ... [fields][field], field name/[data type][data-type] pairs, or
object from which to extract a schema
+#' @examples
+#' # Create schema using pairs of field names and data types
+#' schema(a = int32(), b = float64())
+#'
+#' # Create schema using fields
+#' schema(
+#' field("b", double()),
+#' field("c", bool(), nullable = FALSE),
+#' field("d", string())
+#' )
+#'
+#' # Extract schemas from objects
+#' df <- data.frame(col1 = 2:4, col2 = c(0.1, 0.3, 0.5))
+#' tab1 <- arrow_table(df)
+#' schema(tab1)
+#' tab2 <- arrow_table(df, schema = schema(col1 = int8(), col2 = float32()))
+#' schema(tab2)
+#' @export
+schema <- function(...) {
+ dots <- list2(...)
+
+ if (length(dots) == 1 && !is.list(dots[[1]]) && is.null(names(dots)) &&
!inherits(dots[[1]], "Field")) {
Review Comment:
I think that `length(dots) == 1 && rlang::is_named2(dots[[1]])` may be
sufficient if (1) we add `infer_schema.Field(x, ...) Schema$create(x)` and (2)
we go back to using `!!!items`. If we do allow a single list to be passed as
the first argument, `rlang::is_bare_list()` may be a better choice than
`is.list()` (since `is.list()` will return TRUE for S3 objects that are a list
under the hood like a data.frame).
##########
r/R/schema.R:
##########
@@ -244,10 +230,59 @@ print_schema_fields <- function(s) {
paste(map_chr(s$fields, ~ .$ToString()), collapse = "\n")
}
-#' @param ... [fields][field] or field name/[data type][data-type] pairs
+#' Schemas
+#'
+#' Create a schema or extract one from an object.
+#'
+#' @seealso [Schema] for detailed documentation of the Schema R6 object
+#' @param ... [fields][field], field name/[data type][data-type] pairs, or
object from which to extract a schema
+#' @examples
+#' # Create schema using pairs of field names and data types
+#' schema(a = int32(), b = float64())
+#'
+#' # Create schema using fields
+#' schema(
+#' field("b", double()),
+#' field("c", bool(), nullable = FALSE),
+#' field("d", string())
+#' )
+#'
+#' # Extract schemas from objects
+#' df <- data.frame(col1 = 2:4, col2 = c(0.1, 0.3, 0.5))
+#' tab1 <- arrow_table(df)
+#' schema(tab1)
+#' tab2 <- arrow_table(df, schema = schema(col1 = int8(), col2 = float32()))
+#' schema(tab2)
+#' @export
+schema <- function(...) {
+ dots <- list2(...)
+
+ if (length(dots) == 1 && !is.list(dots[[1]]) && is.null(names(dots)) &&
!inherits(dots[[1]], "Field")) {
+ return(infer_schema(dots[[1]]))
+ }
+
+ Schema$create(...)
+}
+
+#' Create a schema or extract one from an object.
Review Comment:
```suggestion
#' Extract a schema from an object
```
(maybe?)
##########
r/tests/testthat/test-schema.R:
##########
@@ -292,3 +292,9 @@ test_that("schema name assignment", {
expect_identical(names(schm2), c("col1", "col2"))
expect_identical(names(schm2$r_metadata$columns), c("col1", "col2"))
})
+
+test_that("schema extraction", {
+ tbl <- arrow_table(example_data)
+ schema(tbl)
+ expect_equal(schema(tbl), tbl$schema)
+})
Review Comment:
Some other tests that may be useful:
- Test `schema(!!!some_list)` (or `schema(some_list)` if you choose that
direction)
- One test for each type of object that can have a schema extracted with
`schema()`
##########
r/R/schema.R:
##########
@@ -244,10 +230,59 @@ print_schema_fields <- function(s) {
paste(map_chr(s$fields, ~ .$ToString()), collapse = "\n")
}
-#' @param ... [fields][field] or field name/[data type][data-type] pairs
+#' Schemas
+#'
+#' Create a schema or extract one from an object.
+#'
+#' @seealso [Schema] for detailed documentation of the Schema R6 object
+#' @param ... [fields][field], field name/[data type][data-type] pairs, or
object from which to extract a schema
+#' @examples
+#' # Create schema using pairs of field names and data types
+#' schema(a = int32(), b = float64())
+#'
+#' # Create schema using fields
+#' schema(
+#' field("b", double()),
+#' field("c", bool(), nullable = FALSE),
+#' field("d", string())
+#' )
+#'
+#' # Extract schemas from objects
+#' df <- data.frame(col1 = 2:4, col2 = c(0.1, 0.3, 0.5))
+#' tab1 <- arrow_table(df)
+#' schema(tab1)
+#' tab2 <- arrow_table(df, schema = schema(col1 = int8(), col2 = float32()))
+#' schema(tab2)
+#' @export
+schema <- function(...) {
+ dots <- list2(...)
+
+ if (length(dots) == 1 && !is.list(dots[[1]]) && is.null(names(dots)) &&
!inherits(dots[[1]], "Field")) {
+ return(infer_schema(dots[[1]]))
+ }
+
+ Schema$create(...)
+}
+
+#' Create a schema or extract one from an object.
+#'
+#' @param x An object which has a schema, e.g. a `Dataset`
+#' @export
+infer_schema <- function(x) {
+ UseMethod("infer_schema")
+}
+
+#' @export
+infer_schema.ArrowTabular <- function(x) x$schema
+
+#' @export
+infer_schema.RecordBatchReader <- function(x) x$schema
+
+#' @export
+infer_schema.Dataset <- function(x) x$schema
+
Review Comment:
I think you added a way to do this for `data.frame` already that might make
sense to wire up here?
##########
r/R/schema.R:
##########
@@ -244,10 +230,59 @@ print_schema_fields <- function(s) {
paste(map_chr(s$fields, ~ .$ToString()), collapse = "\n")
}
-#' @param ... [fields][field] or field name/[data type][data-type] pairs
+#' Schemas
+#'
+#' Create a schema or extract one from an object.
+#'
+#' @seealso [Schema] for detailed documentation of the Schema R6 object
+#' @param ... [fields][field], field name/[data type][data-type] pairs, or
object from which to extract a schema
+#' @examples
+#' # Create schema using pairs of field names and data types
+#' schema(a = int32(), b = float64())
+#'
+#' # Create schema using fields
+#' schema(
+#' field("b", double()),
+#' field("c", bool(), nullable = FALSE),
+#' field("d", string())
+#' )
+#'
+#' # Extract schemas from objects
+#' df <- data.frame(col1 = 2:4, col2 = c(0.1, 0.3, 0.5))
+#' tab1 <- arrow_table(df)
+#' schema(tab1)
+#' tab2 <- arrow_table(df, schema = schema(col1 = int8(), col2 = float32()))
+#' schema(tab2)
+#' @export
+schema <- function(...) {
+ dots <- list2(...)
+
+ if (length(dots) == 1 && !is.list(dots[[1]]) && is.null(names(dots)) &&
!inherits(dots[[1]], "Field")) {
+ return(infer_schema(dots[[1]]))
+ }
+
+ Schema$create(...)
Review Comment:
```suggestion
Schema$create(!!!dots)
```
(this is what I usually see after capturing a dots expression but I forget
the details/if it matters)
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