将字符向量映射到 r 中的 lm 公式

问题描述

我正在尝试使用 purrr::map 制作一个 lm 对象列表.以 mtcars 为例:

I'm trying to make a list of lm object using purrr::map.use mtcars as an example:

vars <- c('hp', 'wt', 'disp')
map(vars, ~lm(mpg~.x, data=mtcars))

错误:model.frame.default(formula = mpg ~ .x, data = mtcars, drop.unused.levels = TRUE) 中的错误:变量长度不同(找到.x")

error: Error in model.frame.default(formula = mpg ~ .x, data = mtcars, drop.unused.levels = TRUE) : variable lengths differ (found for '.x')

我也试过:

map(vars, function(x) {x=sym(x); lm(mpg~!!x, data=mtcars)})

我收到错误消息:

Error in !x : invalid argument type

谁能告诉我我做错了什么?提前致谢.

Can anyone tell what I did wrong? Thanks in advance.

推荐答案

通常的方式是将公式粘贴作为字符串，通过mapping 进行转换as.formula(您不能制作公式向量；它必须是一个列表)，然后是 map lm.如果您愿意，您可以将它们全部组合到一个调用中，但我更喜欢映射单个函数，这使代码更易于阅读:

The usual way is to paste together formulas as strings, convert them by mapping as.formula (you can't make a vector of formulas; it has to be a list), and then map lm. You can combine it all to a single call if you like, but I've come to prefer mapping single functions, which makes code easier to read:

library(purrr)

c('hp', 'wt', 'disp') %>%
    paste('mpg ~', .) %>%
    map(as.formula) %>%
    map(lm, data = mtcars)
#> [[1]]
#>
#> Call:
#> .f(formula = .x[[i]], data = ..1)
#>
#> Coefficients:
#> (Intercept)           hp
#>    30.09886     -0.06823
#>
#>
#> [[2]]
#>
#> Call:
#> .f(formula = .x[[i]], data = ..1)
#>
#> Coefficients:
#> (Intercept)           wt
#>      37.285       -5.344
#>
#>
#> [[3]]
#>
#> Call:
#> .f(formula = .x[[i]], data = ..1)
#>
#> Coefficients:
#> (Intercept)         disp
#>    29.59985     -0.04122

实际上没有必要调用 map(as.formula) 因为 lm 会将其强制转换为公式，但并非所有模型都如此慷慨(例如 mgcv::gam).

It's actually unnecessary to call map(as.formula) as lm will coerce it into a formula, but not all models are so generous (e.g. mgcv::gam).

这种方法的一个缺点是对象中列出的调用看起来很时髦，但系数告诉你哪个很容易.一个有用的替代方法是将公式作为字符串保存在 data.frame 的一列中，并将模型保存在列表列中，例如

A downside of this approach are that the call listed in the object looks funky, but the coefficients tell you which is which easily enough anyway. A useful alternative is to keep the formula as a string in one column of a data.frame and the model in a list column, e.g.

library(tidyverse)

data_frame(formula = paste('mpg ~', c('hp', 'wt', 'disp')),
           model = map(formula, lm, data = mtcars))
#> # A tibble: 3 x 2
#>      formula    model
#>        <chr>   <list>
#> 1   mpg ~ hp <S3: lm>
#> 2   mpg ~ wt <S3: lm>
#> 3 mpg ~ disp <S3: lm>

这篇关于将字符向量映射到 r 中的 lm 公式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！