ianmcook commented on a change in pull request #11176:
URL: https://github.com/apache/arrow/pull/11176#discussion_r711590655
##########
File path: r/tests/testthat/test-dplyr.R
##########
@@ -989,19 +989,86 @@ test_that("sign()", {
)
})
-test_that("ceiling(), floor(), trunc()", {
+test_that("ceiling(), floor(), trunc(), round()", {
df <- tibble(x = c(-1, -0.55, -0.5, -0.1, 0, 0.1, 0.5, 0.55, 1, NA, NaN))
expect_dplyr_equal(
input %>%
mutate(
c = ceiling(x),
f = floor(x),
- t = trunc(x)
+ t = trunc(x),
+ r = round(x)
) %>%
collect(),
df
)
+
+ # with digits set to 1
+ expect_dplyr_equal(
+ input %>%
+ filter(x %% 0.5 == 0) %>%
+ mutate(r = round(x, 1)) %>%
+ collect(),
+ df
+ )
+
+ # with digits set to -1
+ expect_dplyr_equal(
+ input %>%
+ mutate(
+ rd = round(floor(x * 111), -1), # double
+ y = ifelse(is.nan(x), NA_integer_, x),
+ ri = round(as.integer(y * 111), -1) # integer (with the NaN removed)
+ ) %>%
+ collect(),
+ df
+ )
+
+ # round(x, -2) is equivalent to round_to_multiple(x, 100)
+ expect_equal(
+ Table$create(x = 1111.1) %>%
+ mutate(r = round(x, -2)) %>%
+ collect(),
+ Table$create(x = 1111.1) %>%
+ mutate(r = arrow_round_to_multiple(x, options = list(multiple = 100)))
%>%
+ collect()
+ )
+
+ skip_on_os("windows") # float representation error might cause inconsistency
+
+ expect_dplyr_equal(
+ input %>%
+ mutate(r = round(x, 1)) %>%
+ collect(),
+ df
+ )
+
+ # verify that round mode HALF_TO_EVEN which is what the round() binding uses
+ # yields results consistent with R...
+ expect_equal(
+ as.vector(
+ call_function(
+ "round",
+ Array$create(df$x),
+ options = list(ndigits = 1L, round_mode = RoundMode$HALF_TO_EVEN)
+ )
+ ),
+ round(df$x, 1)
+ )
+ # ... but round mode HALF_TOWARDS_ZERO does not.
Review comment:
The R docs say:
>Note that for rounding off a 5, the IEC 60559 standard (see also ‘IEEE
754’) is expected to be used, ‘go to the even digit’. Therefore round(0.5) is 0
and round(-1.5) is -2. However, this is dependent on OS services and on
representation error (since e.g. 0.15 is not represented exactly, the rounding
rule applies to the represented number and not to the printed number, and so
round(0.15, 1) could be either 0.1 or 0.2).
So R's rounding mode is equivalent to the `HALF_TO_EVEN` mode in Arrow. The
expectation beginning on line 1049 tests that. The expectation beginning on
line 1060 tests the test.
The default tolerance is sufficient to detect that but not detect
floating-point error propagation.
These tests are skipped on CRAN to avoid possible failures on CRAN test
machines that could hypothetically be caused by the dependency of R's rounding
behavior on OS services.
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