函数生成；更改其他功能的默认值(部分) [英] Function generation; change defaults of other functions (partial)

问题描述

我需要一个函数生成器，它接受另一个函数和该函数的任何参数并设置新的默认值.我认为@hadley 的 pryr::partial 就是那个神奇的功能.它完全符合我的要求，除非您无法更改新的默认值.所以在这里我可以在我的新 paste 函数中更改 sep 但不能更改 collapse = "_BAR_" 的新默认值.如何让 partial 以这种方式执行(即，默认为 collapse = "_BAR_" 但如果需要，可以将其设置为 collapse = NULL)?如果 partial 无法做到这一点，有没有办法重写 partial 的代码来做到这一点:https://github.com/hadley/pryr/blob/master/R/partial.r

I have the need for a function generator that takes another function and any arguments of that function and sets new defaults. I thought @hadley's pryr::partial was that magic function. It does exactly what I want except you can't then change that new default. So here I can change sep in my new paste function but not the new default of collapse = "_BAR_". How can I make partial perform this way (i.e., default to collapse = "_BAR_" but enable setting it to collapse = NULL if desired)? If this is not possible with partial is there a way to rewrite the code for partial to do this: https://github.com/hadley/pryr/blob/master/R/partial.r

library(pryr)
.paste <- pryr::partial(paste, collapse = "_FOO_")

.paste(1:5)
.paste(1:5, LETTERS[1:5], sep="_BAR_")
.paste(1:5, collapse=NULL)

> .paste(1:5)
[1] "1_FOO_2_FOO_3_FOO_4_FOO_5"

> .paste(1:5, LETTERS[1:5], sep="_BAR_")
[1] "1_BAR_A_FOO_2_BAR_B_FOO_3_BAR_C_FOO_4_BAR_D_FOO_5_BAR_E"

> .paste(1:5, collapse=NULL)
Error in paste(collapse = "_FOO_", ...) : 
  formal argument "collapse" matched by multiple actual arguments

推荐答案

partial 适合修复某些参数值，但如果您想更改默认值，您可能会考虑不同的策略.这行得通

partial is good for fixing certain parameter values, but if you want to change defaults, you might consider a different strategy. This would work

.paste <- paste
formals(.paste)$collapse <- "_FOO_"

这改变了函数的参数

args(.paste)
# function (..., sep = " ", collapse = "_FOO_") 
# NULL

然后你就可以了

.paste(1:5)
# [1] "1_FOO_2_FOO_3_FOO_4_FOO_5"
.paste(1:5, LETTERS[1:5], sep="_BAR_")
# [1] "1_BAR_A_FOO_2_BAR_B_FOO_3_BAR_C_FOO_4_BAR_D_FOO_5_BAR_E"
.paste(1:5, collapse=NULL)
# [1] "1" "2" "3" "4" "5"

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