创建一个小标题，其中一列是一个函数 [英] create a tibble where one column is a function

问题描述

让我说一下，小标题是这样的:

lets say I have a tibble which looks like this:

library(tidyverse)
tib <- tibble (a = 1:3, b = 4:6, d = -1:1)

我想在此小标题中添加一列，其中每个条目都是具有参数a，b和d的函数(例如f(x)= a x ^ 2 + b x + d).这意味着(例如)在第一行中，我想添加函数f(x)= 1 x ^ 2 + 4 x -1，依此类推.

I want to add a column to this tibble where each entry is a function with parameters a,b and d (like f(x) = ax^2 + bx +d). This would mean that (e.g) in the first row I would like to add the function f(x) = 1 x ^2 + 4 x -1, and so on.

我尝试了以下操作:

tib2 <- tib %>%
   mutate(fun = list(function(x) {a*x^2+b*x+d}))

这不起作用，因为函数不知道a，b和d是什么.

This does not work since the functions do not know what a, b and d are.

我设法使用功能 mapply

lf <- mapply(function(a,b,d){return(function(x){a*x^2 + b*x + d})}, tib$a, tib$b, tib$d)
tib3 <- tib %>% 
  add_column(lf)

我想知道是否有人知道在tidyverse中这样做的更优雅的方式.感觉有一种方法可以使用 purrr 包中的 map 函数，但是我没有设法使其正常工作.

I was wondering if anyone knows a more elegant way of doing this within the tidyverse. It feels like there is a way using the map function from the purrr package, but I did not manage to get it working.

谢谢

推荐答案

在示例中使用 mutate 时，您将为其提供一个包含一个元素(功能)的列表.因此，此功能已为所有其他行回收.此外，在函数的定义内，它对 a ， b 或 d 没有任何可见性.

When you used mutate in your example, you were giving it a list with one element (function). So this one function was recycled for all the other rows. Also, inside the definition of the function, it doesn't have any visibility of a, b or d.

您可以改为使用 pmap ，以便每一行都有其自己的功能.

You can instead use pmap so that each row has its own function.

tib2 <- tib %>%
  mutate(
    fun = pmap(
      list(a, b, d),
      ~function(x) ..1 * x^2 + ..2 * x + ..3))

tib2
#> # A tibble: 3 x 4
#>       a     b     d    fun
#>   <int> <int> <int> <list>
#> 1     1     4    -1  <fun>
#> 2     2     5     0  <fun>
#> 3     3     6     1  <fun>

tib2$fun[[1]](1)
#> [1] 4

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