我正在探索使用data.table包装聚合函数(但实际上它可以是任何类型的函数)的不同方法(也提供了一个dplyr示例),并且想知道关于函数式编程/元编程的最佳实践
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性能(对于data.table可能适用的潜在优化,实现是否重要)
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可读性(有一个共同商定的标准,例如在大多数使用data.table的包中)
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易于推广(元编程的方式是"generalizable")
基本应用是灵活地聚合表,即参数化变量以聚合,聚合的维度,两者的相应结果变量名称和聚合函数 . 我已经在三个data.table和一个dplyr方式中实现了(几乎)相同的功能:
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fn_dt_agg1(这里我无法弄清楚如何参数化聚合函数)
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fn_dt_agg2(灵感来自@jangorecki的答案here,他称之为"computing on the language")
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fn_dt_agg3(灵感来自@Arun的答案here,这似乎是元编程的另一种方法)
-
fn_df_agg1(我在dplyr中的谦虚态度)
libraries
library(data.table)
library(dplyr)
data
n_size <- 1*10^6
sample_metrics <- sample(seq(from = 1, to = 100, by = 1), n_size, rep = T)
sample_dimensions <- sample(letters[10:12], n_size, rep = T)
df <-
data.frame(
a = sample_metrics,
b = sample_metrics,
c = sample_dimensions,
d = sample_dimensions,
x = sample_metrics,
y = sample_dimensions,
stringsAsFactors = F)
dt <- as.data.table(df)
implementations
- fn_dt_agg1
fn_dt_agg1 <-
function(dt, metric, metric_name, dimension, dimension_name) {
temp <- dt[, setNames(lapply(.SD, function(x) {sum(x, na.rm = T)}),
metric_name),
keyby = dimension, .SDcols = metric]
temp[]
}
res_dt1 <-
fn_dt_agg1(
dt = dt, metric = c("a", "b"), metric_name = c("a", "b"),
dimension = c("c", "d"), dimension_name = c("c", "d"))
- fn_dt_agg2
fn_dt_agg2 <-
function(dt, metric, metric_name, dimension, dimension_name,
agg_type) {
j_call = as.call(c(
as.name("."),
sapply(setNames(metric, metric_name),
function(var) as.call(list(as.name(agg_type),
as.name(var), na.rm = T)),
simplify = F)
))
dt[, eval(j_call), keyby = dimension][]
}
res_dt2 <-
fn_dt_agg2(
dt = dt, metric = c("a", "b"), metric_name = c("a", "b"),
dimension = c("c", "d"), dimension_name = c("c", "d"),
agg_type = c("sum"))
all.equal(res_dt1, res_dt2)
#TRUE
- fn_dt_agg3
fn_dt_agg3 <-
function(dt, metric, metric_name, dimension, dimension_name, agg_type) {
e <- eval(parse(text=paste0("function(x) {",
agg_type, "(", "x, na.rm = T)}")))
temp <- dt[, setNames(lapply(.SD, e),
metric_name),
keyby = dimension, .SDcols = metric]
temp[]
}
res_dt3 <-
fn_dt_agg3(
dt = dt, metric = c("a", "b"), metric_name = c("a", "b"),
dimension = c("c", "d"), dimension_name = c("c", "d"),
agg_type = "sum")
all.equal(res_dt1, res_dt3)
#TRUE
- fn_df_agg1
fn_df_agg1 <-
function(df, metric, metric_name, dimension, dimension_name, agg_type) {
all_vars <- c(dimension, metric)
all_vars_new <- c(dimension_name, metric_name)
dots_group <- lapply(dimension, as.name)
e <- eval(parse(text=paste0("function(x) {",
agg_type, "(", "x, na.rm = T)}")))
df %>%
select_(.dots = all_vars) %>%
group_by_(.dots = dots_group) %>%
summarise_each_(funs(e), metric) %>%
rename_(.dots = setNames(all_vars, all_vars_new))
}
res_df1 <-
fn_df_agg1(
df = df, metric = c("a", "b"), metric_name = c("a", "b"),
dimension = c("c", "d"), dimension_name = c("c", "d"),
agg_type = "sum")
all.equal(res_dt1, as.data.table(res_df1))
#"Datasets has different keys. 'target': c, d. 'current' has no key."
benchmarking
出于好奇和我未来的自我和其他感兴趣的各方,我运行了所有4个实现的基准,这可能已经揭示了性能问题(尽管我不是基准专家,所以请原谅我是否通常没有应用商定的最佳做法) . 我期望fn_dt_agg1是最快的,因为它有一个参数少(聚合函数),但似乎没有相当大的影响 . 我也对相对较慢的dplyr功能感到惊讶,但这可能是由于我的设计选择不好 .
library(microbenchmark)
bench_res <-
microbenchmark(
fn_dt_agg1 =
fn_dt_agg1(
dt = dt, metric = c("a", "b"),
metric_name = c("a", "b"),
dimension = c("c", "d"),
dimension_name = c("c", "d")),
fn_dt_agg2 =
fn_dt_agg2(
dt = dt, metric = c("a", "b"),
metric_name = c("a", "b"),
dimension = c("c", "d"),
dimension_name = c("c", "d"),
agg_type = c("sum")),
fn_dt_agg3 =
fn_dt_agg3(
dt = dt, metric = c("a", "b"),
metric_name = c("a", "b"),
dimension = c("c", "d"),
dimension_name = c("c", "d"),
agg_type = c("sum")),
fn_df_agg1 =
fn_df_agg1(
df = df, metric = c("a", "b"), metric_name = c("a", "b"),
dimension = c("c", "d"), dimension_name = c("c", "d"),
agg_type = "sum"),
times = 100L)
bench_res
# Unit: milliseconds
# expr min lq mean median uq max neval
# fn_dt_agg1 28.96324 30.49507 35.60988 32.62860 37.43578 140.32975 100
# fn_dt_agg2 27.51993 28.41329 31.80023 28.93523 33.17064 84.56375 100
# fn_dt_agg3 25.46765 26.04711 30.11860 26.64817 30.28980 153.09715 100
# fn_df_agg1 88.33516 90.23776 97.84826 94.28843 97.97154 172.87838 100
other resources
1 回答
我不推荐
eval(parse())
. 如果没有它,您可以实现与方法三相同:这也避免了一些安全风险 .
PS:您可以通过设置
options("datatable.verbose" = TRUE)
来检查data.table在优化方面做了什么 .