One error you may encounter in R is:
Error: Cannot add ggproto objects together.
Did you forget to add this object to a ggplot object?
This error typically occurs when you attempt to create a visualization using the ggplot2 package but forget to add a plus (+) sign somewhere in the syntax.
This tutorial shares exactly how to fix this error.
How to Reproduce the Error
Suppose we have the following data frame in R that shows the number of total sales and customers that a store receives during 10 different days:
#create data frame df frame(day = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), sales = c(8, 8, 7, 6, 7, 8, 9, 12, 14, 18), customers = c(4, 6, 6, 4, 6, 7, 8, 9, 12, 13)) #view data frame df day sales customers 1 1 8 4 2 2 8 6 3 3 7 6 4 4 6 4 5 5 7 6 6 6 8 7 7 7 9 8 8 8 12 9 9 9 14 12 10 10 18 13
Now suppose we attempt to create a line chart to visualize the sales and customers during each of the 10 days:
library(ggplot2)
#attempt to create plot with two lines
ggplot(df, aes(x = day))
geom_line(aes(y = sales, color = 'sales')) +
geom_line(aes(y = customers, color = 'customers'))
Error: Cannot add ggproto objects together.
Did you forget to add this object to a ggplot object?
We receive an error that tell us we cannot add ggproto objects together.
How to Fix the Error
The way to fix this error is to simply add a plus sign (+) at the end of the first line, which we forgot to do the first time:
library(ggplot2)
#create plot with two lines
ggplot(df, aes(x = day)) +
geom_line(aes(y = sales, color = 'sales')) +
geom_line(aes(y = customers, color = 'customers'))
The result is a plot with two lines that shows the total customers and sales during this 10-day period.
Notice that we don’t receive an error this time because we used a plus sign (+) at the end of the first line.
Additional Resources
The following tutorials explain how to troubleshoot other common errors in R:
How to Fix in R: dim(X) must have a positive length
How to Fix in R: names do not match previous names
How to Fix in R: longer object length is not a multiple of shorter object length
How to Fix in R: contrasts can be applied only to factors with 2 or more levels