如何在mutate中以编程方式使用多项式函数?

问题描述

我想使用mutate根据预先定义的具有二次/多项式函数的变量为我提供预测值.我可以使用这样的线性公式轻松地做到这一点:

I want to use mutate to give me predicted values based on pre-specified variables with a quadratic / polynomial function. I can easily do this with a linear formula like this:

library(tidyverse)

xvar <- "Sepal.Length"
yvar <- "Sepal.Width"


##linear fit
#what does formula text look like?
formula = !!sym(yvar) ~ !!sym(xvar)
formula

models <- iris %>%
  nest(-Species) %>%
  mutate(
    # Perform loess (or lm) calculation on each  group
    m = map(data, lm,
            formula = !!sym(yvar) ~ !!sym(xvar) ),
    # Retrieve the fitted values from each model
    fitted = map(m, `[[`, "fitted.values")
  )

但是，尝试使用多项式公式建模会产生错误.我在做什么错了?

However, trying to model with a polynomial formula creates an error. What am I doing wrong?

##polynomial fit

#what does formula text look like?
formula = !!sym(yvar) ~ !!sym(xvar) + I(!!sym(xvar)^2)
formula

#Doesn't work
models <- iris %>%
  nest(-Species) %>%
  mutate(
    # Perform loess (or lm) calculation on each  group
    m = map(data, lm,
            formula = !!sym(yvar) ~ !!sym(xvar) + I(!!sym(xvar)^2)),
            #formula = Sepal.Length ~ Sepal.Width + I(Sepal.Width^2)), #works
    # Retrieve the fitted values from each model
    fitted = map(m, `[[`, "fitted.values")
  )

#Error in sym(xvar)^2 : non-numeric argument to binary operator

推荐答案

您是否尝试过将方括号放在其他位置?例如sym(xvar ^ 2)还是(!!sym(xvar)) ^ 2?

Have you tried putting the brackets in different places? e.g. sym(xvar ^ 2) or (!!sym(xvar)) ^ 2?

错误消息告诉您sym(xvar)是非数字的，这是正确的.因此，您需要应用一元！运算符之前的二进制^一.

The error messages is telling you that sym(xvar) is non numeric, which is true. So you need to apply the unary !! operator before the binary ^ one.

操作员优先级:

https://stat.ethz .ch/R-manual/R-devel/library/base/html/Syntax.html

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