display multiple plots in a list using grid.arrange in R

Question

I want to display multiple plots depending on the length of my predictors. I have created two list and then used grid.arrange function to display the plots within these lists, but I am getting the following error message -'only 'grobs' allowed in "gList". Even when I try to use only one list say p, I get the same error message. Please help!

 library(ggplot2)
 library(gridExtra)


 # dependent1 variable
 # dependent2 variable 
 # predictor_vector is a vector of predictors

 plot_output(data, dependent1, dependent2, predictor_vector)
 {

 length<-length(predictor_vector)

  p<-list()
  g<-list()

  for( i in 1:length)
  {
  p[[i]]<-ggplot(data, aes(y=dependent1, x=predictor_vector[i]))
  g[[i]]<-ggplot(data, aes(y=dependent2, x=predictor_vector[i]))
  }


  do.call("grid.arrange", c(p, g, list(ncol=2)))

 }

Answer 1

Posting as an answer only to show the example that's impossible in a comment.

The idiom you're trying to use is correct:

library(ggplot2)
library(gridExtra)

p <- list(ggplot(mtcars, aes(x=wt, y=mpg))+geom_point(col="black"),
          ggplot(mtcars, aes(x=wt, y=mpg))+geom_point(col="orange"),
          ggplot(mtcars, aes(x=mpg, y=wt))+geom_point(col="blue"))

g <- list(ggplot(mtcars, aes(x=wt, y=mpg))+geom_point(col="red"),
          ggplot(mtcars, aes(x=mpg, y=wt))+geom_point(col="green"))

do.call(grid.arrange, c(p, g, list(ncol=2)))

Two variable length ggplot object lists and then the parameter list. You need to provide the data and a more complete loop for us to know how to help you figure out what you're doing incorrectly.