r-将函数应用于数据n次 [英] r - apply a function on data n number of times
问题描述
我想每次使用函数的输出将相同的函数多次应用到矢量上.
I would like to apply the same function certain number of times on a vector using the output from the function every time.
具有简单功能的简化示例仅用于演示:
A simplified example with a simple function just to demonstrate:
# sample vector
a <- c(1,2,3)
# function to be applied n times
f1 <- function(x) {
x^2 + x^3
}
我想将f1
应用于a
,n
次数,例如在这里说3次.
I would like to apply f1
on a
, n
number of times, for example here lets say 3 times.
我听说purrr::reduce
或purrr::map()
可能是个好主意,但无法使其正常工作.
I heard purrr::reduce
or purrr::map()
might be a good idea for this but couldn't make it work.
n = 3
等于f1(f1(f1(a)))
时所需的输出.
推荐答案
让我们使用Reduce
(无外部库要求,总体性能良好).我将稍微修改该函数以接受第二个(忽略的)参数:
Let's use Reduce
(no external library requirements, generally good performance). I'll modify the function slightly to accept a second (ignored) argument:
f1 <- function(x, ign) x^2 + x^3
Reduce(f1, 1:3, init = a)
# [1] 1.872000e+03 6.563711e+09 1.102629e+14
这是正在发生的事情. Reduce
:
Here's what's happening. Reduce
:
使用二进制函数将给定向量的元素和可能给定的初始值相继合并.
uses a binary function to successively combine the elements of a given vector and a possibly given initial value.
第一个参数是要使用的函数,它应该接受两个参数.第一个是此简化中函数上一个执行的值.在第一次调用该函数时,它将使用提供的init=
值.
The first argument is the function to use, and it should accept two arguments. The first is the value from the previous execution of the function in this reduction. On the first call of the function, it uses the init=
value provided.
-
首次通话:
First call:
f1(c(1,2,3), 1)
# [1] 2 12 36
第二通电话:
Second call:
f1(c(2,12,36), 2)
# [1] 12 1872 47952
第三次通话:
Third call:
f1(c(12,1872,47952), 3)
# [1] 1.872000e+03 6.563711e+09 1.102629e+14
第二个参数1:3
仅用于其长度.适当长度的任何东西都可以使用.
The second argument 1:3
is used just for its length. Anything of the proper length will work.
如果您不只是为了减少此操作而重新定义f1
,您始终可以
If you don't want to redefine f1
just for this reduction, you can always do
Reduce(function(a,ign) f1(a), ...)
基准:
Benchmark:
library(microbenchmark)
r <- Reduce(function(a,b) call("f1", a), 1:3, init=quote(a))
triple_f1 <- function(a) f1(f1(f1(a)))
microbenchmark::microbenchmark(
base = Reduce(function(a,ign) f1(a), 1:3, a),
accum = a %>% accumulate(~ .x %>% f1, .init = f1(a)) %>% extract2(3),
reduc = purrr::reduce(1:3, function(a,ign) f1(a), .init=a),
whil = {
i <- 1
a <- c(1,2,3)
while (i < 10) {
i <- i + 1
a <- f1(a)
}
},
forloop = {
out <- a
for(i in seq_len(3)) out <- f1(out)
},
evaluated = {
r <- Reduce(function(a,b) call("f1", a), 1:3, init=quote(a))
eval(r)
},
precompiled = eval(r),
anotherfun = triple_f1(a)
)
# Unit: microseconds
# expr min lq mean median uq max neval
# base 5.101 7.3015 18.28691 9.3010 10.8510 848.302 100
# accum 294.201 328.4015 381.21204 356.1520 402.6510 823.602 100
# reduc 27.000 38.1005 57.55694 45.2510 54.2005 747.401 100
# whil 1717.300 1814.3510 1949.03100 1861.8510 1948.9510 2931.001 100
# forloop 1110.001 1167.1010 1369.87696 1205.5010 1292.6500 9935.501 100
# evaluated 6.702 10.2505 22.18598 13.3015 15.5510 715.301 100
# precompiled 2.300 3.2005 4.69090 4.0005 4.5010 26.800 100
# anotherfun 1.400 2.0515 12.85201 2.5010 3.3505 1017.801 100
这篇关于r-将函数应用于数据n次的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!