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More Efficient group_by(...) %>% sample_*(...) #3193

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merged 2 commits into from Dec 30, 2017
Merged

More Efficient group_by(...) %>% sample_*(...) #3193

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ce4ba23
More Efficient `group_by(...) %>% sample_*(...)`
Nov 6, 2017
7de3757
Merge branch 'master' into efficient_sample_group
krlmlr Dec 30, 2017
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2 changes: 2 additions & 0 deletions NEWS.md
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Expand Up @@ -45,6 +45,8 @@

* Add error for `distinct()` if any of the selected columns are of type `list` (#3088, @foo-bar-baz-qux).

* `sample_n()` and `sample_frac()` on grouped data frame are now faster especially for those with large number of groups (#3193, @saurfang).

* Better error message if dbplyr is not installed when accessing database backends (#3225).

* Fix `row_number()` and `ntile()` ordering to use the locale-dependent ordering functions in R when dealing with character vectors, rather than always using the C-locale ordering function in C (#2792, @foo-bar-baz-qux).
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9 changes: 4 additions & 5 deletions R/grouped-df.r
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Expand Up @@ -265,11 +265,11 @@ sample_n.grouped_df <- function(tbl, size, replace = FALSE,
inform("`.env` is deprecated and no longer has any effect")
}
weight <- enquo(weight)
weight <- mutate(tbl, w = !!weight)[["w"]]
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Could you add a space after the !! please?

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Nevermind, !! is going to have very high precedence so now it makes sense to have it close to its argument just like unary -.

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Great. Let me know if there is anything else I can help to help this PR merged.


index <- attr(tbl, "indices")
sampled <- lapply(index, sample_group,
frac = FALSE,
tbl = tbl,
size = size,
replace = replace,
weight = weight
Expand All @@ -292,11 +292,11 @@ sample_frac.grouped_df <- function(tbl, size = 1, replace = FALSE,
)
}
weight <- enquo(weight)
weight <- mutate(tbl, w = !!weight)[["w"]]

index <- attr(tbl, "indices")
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It looks a bit cleaner (and maybe faster) if we assign index <- attr(...) + 1L here and don't add in sample_group().

sampled <- lapply(index, sample_group,
frac = TRUE,
tbl = tbl,
size = size,
replace = replace,
weight = weight
Expand All @@ -306,7 +306,7 @@ sample_frac.grouped_df <- function(tbl, size = 1, replace = FALSE,
grouped_df(tbl[idx, , drop = FALSE], vars = groups(tbl))
}

sample_group <- function(tbl, i, frac, size, replace, weight) {
sample_group <- function(i, frac, size, replace, weight) {
n <- length(i)
if (frac) {
check_frac(size, replace)
Expand All @@ -315,9 +315,8 @@ sample_group <- function(tbl, i, frac, size, replace, weight) {
check_size(size, n, replace)
}

weight <- eval_tidy(weight, tbl[i + 1, , drop = FALSE])
if (!is_null(weight)) {
weight <- check_weight(weight, n)
weight <- check_weight(weight[i + 1], n)
}

i[sample.int(n, size, replace = replace, prob = weight)]
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