[arrow] branch main updated: GH-37842: [R] Implement infer_schema.data.frame() (#37843)

[thisisnic]

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The following commit(s) were added to refs/heads/main by this push:
     new 79abb7362f GH-37842: [R] Implement infer_schema.data.frame() (#37843)
79abb7362f is described below

commit 79abb7362f671f484675b89f19566df861c45f6f
Author: Nic Crane <thisis...@gmail.com>
AuthorDate: Thu Sep 28 21:40:45 2023 +0100

    GH-37842: [R] Implement infer_schema.data.frame() (#37843)
    
    ### Rationale for this change
    
    Users will be able to easily see the schema which their `data.frame` object 
will have when it's converted into an Arrwo table.
    
    ### What changes are included in this PR?
    
    Implements `infer_schema()` method for `data.frame` objects.
    
    Before:
    
    ``` r
    library(arrow)
    schema(mtcars)
    #> Error in UseMethod("infer_schema"): no applicable method for 
'infer_schema' applied to an object of class "data.frame"
    ```
    After:
    
    ``` r
    library(arrow)
    schema(mtcars)
    #> Schema
    #> mpg: double
    #> cyl: double
    #> disp: double
    #> hp: double
    #> drat: double
    #> wt: double
    #> qsec: double
    #> vs: double
    #> am: double
    #> gear: double
    #> carb: double
    #>
    #> See $metadata for additional Schema metadata
    ```
    
    ### Are these changes tested?
    
    Yes
    
    ### Are there any user-facing changes?
    
    Yes
    * Closes: #37842
    
    Authored-by: Nic Crane <thisis...@gmail.com>
    Signed-off-by: Nic Crane <thisis...@gmail.com>
---
 r/NAMESPACE                    | 1 +
 r/R/schema.R                   | 3 +++
 r/tests/testthat/test-schema.R | 5 +++++
 3 files changed, 9 insertions(+)

diff --git a/r/NAMESPACE b/r/NAMESPACE
index 21f88b4180..d49255f781 100644
--- a/r/NAMESPACE
+++ b/r/NAMESPACE
@@ -112,6 +112,7 @@ S3method(infer_schema,ArrowTabular)
 S3method(infer_schema,Dataset)
 S3method(infer_schema,RecordBatchReader)
 S3method(infer_schema,arrow_dplyr_query)
+S3method(infer_schema,data.frame)
 S3method(infer_type,ArrowDatum)
 S3method(infer_type,Expression)
 S3method(infer_type,blob)
diff --git a/r/R/schema.R b/r/R/schema.R
index 1ad18e3141..ac0604b2b3 100644
--- a/r/R/schema.R
+++ b/r/R/schema.R
@@ -285,6 +285,9 @@ infer_schema.Dataset <- function(x) x$schema
 #' @export
 infer_schema.arrow_dplyr_query <- function(x) implicit_schema(x)
 
+#' @export
+infer_schema.data.frame <- function(x) schema(!!!lapply(x, infer_type))
+
 #' @export
 names.Schema <- function(x) x$names
 
diff --git a/r/tests/testthat/test-schema.R b/r/tests/testthat/test-schema.R
index db91cee330..b1dc065929 100644
--- a/r/tests/testthat/test-schema.R
+++ b/r/tests/testthat/test-schema.R
@@ -295,9 +295,14 @@ test_that("schema name assignment", {
 
 test_that("schema extraction", {
   skip_if_not_available("dataset")
+
   tbl <- arrow_table(example_data)
+  expect_equal(schema(example_data), tbl$schema)
   expect_equal(schema(tbl), tbl$schema)
 
+  expect_equal(schema(data.frame(a = 1, a = "x", check.names = FALSE)), 
schema(a = double(), a = string()))
+  expect_equal(schema(data.frame()), schema())
+
   ds <- InMemoryDataset$create(example_data)
   expect_equal(schema(ds), ds$schema)