context("Sample")
# Basic behaviour -------------------------------------------------------------
test_that("sample preserves class", {
expect_is(sample_n(mtcars, 1), "data.frame")
expect_is(sample_n(tbl_df(mtcars), 1), "tbl_df")
expect_is(sample_frac(mtcars, 1), "data.frame")
expect_is(sample_frac(tbl_df(mtcars), 1), "tbl_df")
})
# Ungrouped -------------------------------------------------------------------
df <- data.frame(
x = 1:2,
y = c(0, 1)
)
test_that("sample respects weight", {
expect_error(sample_n(df, 2, weight = y), "too few positive probabilities")
expect_equal(sample_n(df, 1, weight = y)$x, 2)
expect_error(sample_frac(df, 1, weight = y), "too few positive probabilities")
expect_equal(sample_frac(df, 0.5, weight = y)$x, 2)
})
test_that("sample gives informative error for unknown type", {
expect_error(sample_n(list()), "Don't know how to sample")
})
# Grouped ----------------------------------------------------------------------
test_that("sampling grouped tbl samples each group", {
sampled <- mtcars %>% group_by(cyl) %>% sample_n(2)
expect_is(sampled, "grouped_df")
expect_equal(groups(sampled), list(quote(cyl)))
expect_equal(nrow(sampled), 6)
expect_equal(sampled$cyl, rep(c(4, 6, 8), each = 2))
})
test_that("can't sample more values than obs (without replacement)", {
by_cyl <- mtcars %>% group_by(cyl)
expect_error(sample_n(by_cyl, 10), "Do you want replace = TRUE")
})
df2 <- data.frame(
x = rep(1:2, 2),
y = rep(c(0, 1), 2),
g = rep(1:2, each = 2)
)
test_that("grouped sample respects weight", {
grp <- df2 %>% group_by(g)
expect_error(sample_n(grp, 2, weight = y), "too few positive probabilities")
expect_equal(sample_n(grp, 1, weight = y)$x, c(2, 2))
expect_error(sample_frac(grp, 1, weight = y), "too few positive probabilities")
expect_equal(sample_frac(grp, 0.5, weight = y)$x, c(2, 2))
})
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