如何直接在purrr :: accumulate2()内部编写自定义函数 [英] How to write a custom function directly inside purrr::accumulate2()

问题描述

我只是尝试使用purrr家族的lambda函数.

I am just trying my hands on lambda functions of purrr family.

假设我必须通过 accumulate 对向量中先前迭代的结果进行迭代操作，可以通过.x和.y进行，其中.x是对先前元素和应用的结果.y是当前元素.还要假设函数/迭代次数是 2x + 3y ，即将先前的结果加倍并添加当前元素的三倍，可以通过like来完成.

Suppose I have to do some operation iteratively over result of previous iteration in vector through accumulate I can do it through .x and .y, where .x is result of application on previous element and .y is current element. Also assume that the function/iteration is 2x+3y i.e. double the previous result and add three times of current element, it can be done through like.

accumulate(1:10, ~2*.x + 3*.y)
 [1]    1    8   25   62  139  296  613 1250 2527 5084

#OR
accumulate(1:10, ~2*.x + 3*.y, .init = 2.5)
 [1]    2.5    8.0   22.0   53.0  118.0  251.0  520.0 1061.0 2146.0 4319.0 8668.0

但是，我无法在 accumulate2

accumulate2(1:5, 1:5, ~2*.x + 3*.y +.z)
Error in reduce2_impl(.x, .y, .f, ..., .init = .init, .acc = TRUE) : 
  `.y` does not have length 4

OR

accumulate2(1:5, 1:4, ~2*.x + 3*.y +.z)
Error in .f(out, .x[[x_i]], .y[[y_i]], ...) : object '.z' not found

我实际上从 purrr :: accumulate()了解到的是，它是一个两个参数的函数，其中第一个参数是先前迭代的结果，第二个参数是直接传递给它的向量.在类似的行上， accumulate2()是一个三参数函数，其中第一个参数是先前计算的结果，而其他两个参数则直接传递.

What actually I understood from purrr::accumulate() was that, it is a two argument function where first argument is result of previous iteration and second argument is vector passed into it directly. On similar lines accumulate2() is a three argument function where first argument is result of previous computation and other two arguments are passed directly.

有人可以说出我在理解逻辑上错了什么地方或哪里错了，或者什么是正确的做事方式.

Can someone tell where I am erring or am wrong in understanding the logic or what should be the correct way of doing it.

推荐答案

仅当有两个参数时，才指定 .x 和 .y .超过2个时，我们可以按出现的顺序使用 .. 1 ， .. 2 ， .. 3

The .x and .y are only specified when there are two arguments. With more than 2, we can use ..1, ..2, ..3 in their order of occurrence

library(purrr)
accumulate2(1:5, 1:4, ~2*..1 + 3*..2 +..3)
#[[1]]
#[1] 1

#[[2]]
#[1] 9

#[[3]]
#[1] 29

#[[4]]
#[1] 73

#[[5]]
#[1] 165

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