How to pass variables from lm object to aes(x =, y = )?-CodePudding

Context: I have a function that takes an object created with stats::lm() as its main argument. The goal of this function is to make ggplots with only this lm object. Warning: variables used in the model are NOT arguments of the function i.e. if the model is lmobj <- lm(y ~ x, data = df) then the function only takes lmobj as an argument. Indeed it is different from question like this one. Moreover, I am not looking for "ggplot only" solutions that take the raw data and compute regression line and scatterplot (e.g. ggplot2::geom_smooth(method = "lm")).

Problem: ggplot() geom functions have a x and y argument that require unquoted variables (see reference manual); how can I recover these from lmobj?

Expected output:

library(ggplot2)
lmobj <- lm(Petal.Width ~ Petal.Length, data = iris)
myfun <- function(.lm) {
  # make a scatterplot with .lm using ggplot
  ggplot(data = .lm[["model"]], aes(x = Petal.Width, y = Petal.Length))  
    geom_point()
}
myfun(lmobj)

Trials and errors

I tried to grab an unquoted variable name from lmobject using cat():

> cat(names(lmobj[["model"]][2]))
Petal.Length

But it creates an error:

> myfuntest <- function(.lm) {
    # make a scatterplot with .lm using ggplot
    ggplot(data = .lm[["model"]], aes(x = cat(names(.lm[["model"]][2])), 
                                      y = cat(names(.lm[["model"]][1]))))  
      geom_point()
  }
> myfuntest(lmobj)
Petal.LengthPetal.WidthPetal.LengthPetal.WidthError: geom_point requires the following missing aesthetics: x and y

CodePudding user response：

The following works:

myfun <- function(model) {
  coefs <- names(model$model)
  ggplot(data = model$model)  
    aes(x = !! rlang::sym(coefs[1L]), y = !! rlang::sym(coefs[2L])))  
    geom_point()
}

The relevant point here is that aes uses ‘rlang’s tidy evaluation and as such requires the arguments to be injected via !! as names.

CodePudding user response：

One way to do it is to evaluate first the arguments of aes as symbols and then call aes by wrapping it into a do.call

myfun <- function(.lm) {
  ggplot(data = .lm[["model"]],
         do.call(aes, list(x = sym(names(.lm[["model"]])[2]),
                           y = sym(names(.lm[["model"]])[1]))))  
    geom_point()
}