How do I loop a qqplot in ggplot2?

Question

I am trying to create a function that loops through the columns of my dataset and saves a qq-plot of each of my variables. I have spent a lot of time looking for a solution, but I am an R novice and haven't been able to successfully apply any answers to my data. Can anyone see what I am doing wrong?

There error I am give is this, "Error in eval(expr, envir, enclos) : object 'i' not found"

library(ggplot2)
QQPlot <- function(x, na.rm = TRUE, ...) {
    nm <- names(x)
    for (i in names(mybbs)) {
            plots <-ggplot(mybbs, aes(sample = nm[i])) + 
                    stat_qq()
            ggsave(plots, filename = paste(nm[i], ".png", sep=""))
    }
}

QQPlot(mybbs)

scoa · Accepted Answer · 2015-08-23 17:28:52Z

1

The error happens because you are trying to pass a string as a variable name. Use aes_string() instead of aes()

Moreover, you are looping over names, not indexes; nm[i] would work for something like for(i in seq_along(names(x)), but not with your current loop. You would be better off replacing all nm[i] by i in the function, since what you want is the variable name.

Finally, you use mybbs instead of x inside the function. That means it will not work properly with any other data.frame.

Here is a solution to those three problems:

QQPlot <- function(x, na.rm = TRUE, ...) {
  for (i in names(x)) {
    plots <-ggplot(x, aes_string(sample = i)) + 
      stat_qq()
    #print(plots)
    ggsave(plots, filename = paste(i, ".png", sep=""))
  }
}

edited Aug 23, 2015 at 17:28

answered Aug 23, 2015 at 14:59

scoa

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1 Comment

Hannah Ertl Over a year ago

Thank you for helping me understand my errors and for the code to fix them! It worked like a charm!

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