使用dplyr执行bootstrap复制

Question

我有兴趣使用dplyr来构建bootstrap复制(重复分析,其中每次首次采样替换数据).Hadley Wickham 在这里提供了一些有效重复引导分析的代码:

bootstrap <- function(df, m) {
  n <- nrow(df)

  attr(df, "indices") <- replicate(m, sample(n, replace = TRUE), 
    simplify = FALSE)
  attr(df, "drop") <- TRUE
  attr(df, "group_sizes") <- rep(n, m)
  attr(df, "biggest_group_size") <- n
  attr(df, "labels") <- data.frame(replicate = 1:m)
  attr(df, "vars") <- list(quote(boot)) # list(substitute(bootstrap(m)))
  class(df) <- c("grouped_df", "tbl_df", "tbl", "data.frame")

  df
}

library(dplyr)
mboot <- bootstrap(mtcars, 10)

# Works
mboot %.% summarise(mean(cyl))

虽然此函数适用于此功能summarise,但它do在do包含data.frame 时不起作用.(想象一下,data.frame包含一些有用的东西,比如我们希望引导的分析结果).

bootstrap(mtcars, 3) %>% do(data.frame(x=1:2))
# Error: index out of bounds

跟踪

11: stop(list(message = "index out of bounds", call = NULL, cppstack = NULL))
10: .Call("dplyr_grouped_df_impl", PACKAGE = "dplyr", data, symbols, 
        drop)
9: grouped_df_impl(data, unname(vars), drop)
8: grouped_df(cbind_list(labels, out), groups)
7: label_output_dataframe(labels, out, groups(.data))
6: do.grouped_df(`bootstrap(mtcars, 3)`, data.frame(x = 1:2))
5: do(`bootstrap(mtcars, 3)`, data.frame(x = 1:2))
4: eval(expr, envir, enclos)
3: eval(e, env)
2: withVisible(eval(e, env))
1: bootstrap(mtcars, 3) %>% do(data.frame(x = 1:2))

我能够通过执行两个do步骤和一组来解决这个问题:

bootstrap(mtcars, 10) %>% do(d=data.frame(x=1:2)) %>% group_by(replicate) %>% do(.$d[[1]])

但这似乎需要很多额外的,有些笨拙的步骤(并且还会得到警告Grouping rowwise data frame strips rowwise nature).我也知道我可以先用类似的东西将数据复制到十次复制中

data.frame(boot=1:10) %>% group_by(boot) %>% do(sample_n(mtcars, nrow(mtcars), replace=TRUE))

但是如果数据或引导复制的数量很大,则这在内存中效率极低.

有没有办法,也许通过改变bootstrap设置功能,我可以执行这些重复bootstrap(mtcars, 3) %>% do(data.frame(x = 1:2))？

Answer 1

我认为这是bootstrap函数中的一个小错误.该vars属性应该在比赛中列名data.frame的labels属性.但是在函数中,vars调用属性"boot",列名是replicate.所以,如果你做了这个小改动:

bootstrap <- function(df, m) {
  n <- nrow(df)

  attr(df, "indices") <- replicate(m, sample(n, replace = TRUE), 
                                   simplify = FALSE)
  attr(df, "drop") <- TRUE
  attr(df, "group_sizes") <- rep(n, m)
  attr(df, "biggest_group_size") <- n
  attr(df, "labels") <- data.frame(replicate = 1:m)
  attr(df, "vars") <- list(quote(replicate)) # Change
#  attr(df, "vars") <- list(quote(boot)) # list(substitute(bootstrap(m)))
  class(df) <- c("grouped_df", "tbl_df", "tbl", "data.frame")

  df
}

然后它按预期工作:

bootstrap(mtcars, 3) %>% do(data.frame(x=1:2))
# Source: local data frame [6 x 2]
# Groups: replicate

#   replicate x
# 1         1 1
# 2         1 2
# 3         2 1
# 4         2 2
# 5         3 1
# 6         3 2