如何多次运行一个函数并将结果写入列表? [英] How to run a function multiple times and write the results to a list?

问题描述

我有一个创建矩阵的函数，因此我想调用此函数一千次，最终得到1000个矩阵的列表.这是一个示例:

I have a function that creates a matrix and I want to call this function a thousand times such that in the end I have a list of 1000 matrices. Here is an example:

set.seed(1)
gen_mat <- function(x) matrix(c(1, 1, 1, x + rnorm(1)), nrow = 2)

现在，我尝试了replicate(10, gen_mat(1))，但这将返回一个数组而不是一个列表.怎么做?

Now, I tried replicate(10, gen_mat(1)), but this returns an array and not a list. How to do it?

推荐答案

上述答案，评论和我自己的答案的组合.自然，我更喜欢我的.另外，我认为上述base R的答案有误.

Combination of above answer, comment, and my own answer. Naturally, I like mine better. Also, I think there is a mistake in the above answer for base R.

n <- 10

# give 1 to gen_mat n-times
lapply(rep(1, n), gen_mat)

# replicate n-times 
replicate(n, gen_mat(1), simplify=FALSE)

# lapply returns error if FUN is not function or 
# the function is not taking an argument. Hence a dummy function.
lapply(seq_len(n), function(x) gen_mat(1))

对三种方法进行微基准测试

我为n使用了较大的值，但是在我的桌面中，较小的n也得到了类似的结果.为此，replicate比其他两种方法花费的时间更长.

I used a larger value for n, but the results are similar in my desktop with smaller n as well. For this, replicate takes longer than the other two methods.

set.seed(1)
gen_mat <- function(x) matrix(c(1, 1, 1, x + rnorm(1)), nrow = 2)
n <- 1000 

library(microbenchmark)
library(ggplot2)

mb <- microbenchmark(
  lap1 = {lapply(rep(1, n), gen_mat)},
  repl = {replicate(n, gen_mat(1), simplify=FALSE)},
  lap2 = {lapply(seq_len(n), function(x) gen_mat(1))},
  times = 10000L
)

mb
# Unit: milliseconds
# expr      min       lq     mean   median       uq      max neval cld
# lap1 2.839435 3.494157 4.806954 3.854269 5.611413 103.0111 10000  a 
# repl 3.091829 3.777199 5.140789 4.165856 6.013591 101.4318 10000   b
# lap2 3.131491 3.761274 5.089170 4.140316 5.939075 101.1983 10000   b

autoplot(mb)

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