ianmcook commented on a change in pull request #1:
URL: https://github.com/apache/arrow-cookbook/pull/1#discussion_r674987774
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File path: r/content/reading_and_writing_data.Rmd
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+# Reading and Writing Data
+
+This chapter contains recipes related to reading and writing data from disk
using Apache Arrow.
+
+## Reading and Writing Parquet Files
+
+### Writing a Parquet file
+
+You can write Parquet files to disk using `arrow::write_parquet()`.
+```{r, write_parquet}
+# Create table
+my_table <- Table$create(tibble::tibble(group = c("A", "B", "C"), score =
c(99, 97, 99)))
+# Write to Parquet
+write_parquet(my_table, "my_table.parquet")
+```
+```{r, test_write_parquet, opts.label = "test"}
+test_that("write_parquet chunk works as expected", {
+ expect_true(file.exists("my_table.parquet"))
+})
+```
+
+### Reading a Parquet file
+
+Given a Parquet file, it can be read back to an Arrow Table by using
`arrow::read_parquet()`.
+
+```{r, read_parquet}
+parquet_tbl <- read_parquet("my_table.parquet")
+head(parquet_tbl)
+```
+```{r, test_read_parquet, opts.label = "test"}
+test_that("read_parquet works as expected", {
+ expect_equivalent(dplyr::collect(parquet_tbl), tibble::tibble(group = c("A",
"B", "C"), score = c(99, 97, 99)))
+})
+```
+
+If the argument `as_data_frame` was set to `TRUE` (the default), the file was
read in as a `data.frame` object.
+
+```{r, read_parquet_2}
+class(parquet_tbl)
+```
+```{r, test_read_parquet_2, opts.label = "test"}
+test_that("read_parquet_2 works as expected", {
+ expect_s3_class(parquet_tbl, "data.frame")
+})
+```
+If you set `as_data_frame` to `FALSE`, the file will be read in as an Arrow
Table.
+
+```{r, read_parquet_table}
+my_table_arrow_table <- read_parquet("my_table.parquet", as_data_frame = FALSE)
+head(my_table_arrow_table)
+```
+
+```{r, read_parquet_table_class}
+class(my_table_arrow_table)
+```
+```{r, test_read_parquet_table_class, opts.label = "test"}
+test_that("read_parquet_table_class works as expected", {
+ expect_s3_class(my_table_arrow_table, "Table")
+})
+```
+
Review comment:
Provide some explanation here about why one might want to read in a file
as an Arrow Table instead of an R data frame (lower memory usage, faster
performance, etc.) and say that you can always convert an Arrow Table to an R
data frame by calling either `as.data.frame()` or `dplyr::collect()`
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