使用ggridges绘制joyplot时报错：Error in -x : invalid argument to unary operator

Hey there! Let’s work through this frustrating error you’re hitting while trying to make a time-based density joyplot with ggridges and your Dados empilhados dataset. This error almost always boils down to R trying to use a unary minus (-x) on something that isn’t a numeric value—let’s break down the most common fixes:

Common Causes & Solutions #

1. Your grouping/time column isn’t formatted correctly #

ggridges relies on discrete groups (like time periods) for the y-axis of a joyplot. If your time column is stored as a numeric type when it should be a factor/character, or has unexpected values, R can throw this error.

• First, check your column types with:

  str(Dados_empilhados)
  

• If your time column (e.g., Month, Year) is numeric, convert it to a factor:

  Dados_empilhados$time_column <- as.factor(Dados_empilhados$time_column)
  

• For date columns, use lubridate to parse them first, then convert to a factor if you want discrete time groups:

  library(lubridate)
  Dados_empilhados$date_column <- ymd(Dados_empilhados$date_column)
  Dados_empilhados$year_group <- as.factor(year(Dados_empilhados$date_column))
  

2. Your numeric density column has non-numeric values #

The x-axis of your density plot needs to be numeric. If there are characters, NAs, or other non-numeric entries in this column, R can’t perform the density calculation (which uses -x internally).

• Check for non-numeric entries and NAs:

  # Count non-numeric values
  sum(!is.numeric(Dados_empilhados$density_column))
  # Count missing values
  sum(is.na(Dados_empilhados$density_column))
  

• Clean up the column: convert non-numeric values to NA, then add na.rm = TRUE to your geom to skip missing data:

  # Convert non-numeric to NA
  Dados_empilhados$density_column <- as.numeric(Dados_empilhados$density_column)
  # Update your plot code
  ggplot(Dados_empilhados, aes(x = density_column, y = time_column)) +
    geom_density_ridges(na.rm = TRUE) +
    theme_ridges()
  

3. You mixed up x/y aesthetics or used invalid columns #

Double-check your ggplot syntax—make sure you’re mapping a numeric column to x (for density) and a discrete group column to y. A valid joyplot structure should look like this:

library(ggplot2)
library(ggridges)

ggplot(Dados_empilhados, aes(x = your_numeric_data, y = your_time_groups)) +
  geom_density_ridges() +
  labs(title = "Time-Based Density Joyplot", x = "Value", y = "Time Period") +
  theme_ridges()

If you accidentally put a non-numeric column on the x axis, R will try to run density calculations on it, leading to the -x error.

4. You have spaces in column names #

If your dataset has column names with spaces (like your filename), you need to wrap them in backticks when referencing them in aes():

ggplot(Dados_empilhados, aes(x = `Numeric Value With Spaces`, y = `Time Period`)) +
  geom_density_ridges()

Without backticks, R misinterprets space-separated names as multiple columns.

If none of this works… #

Share a snippet of your data (use dput(head(Dados_empilhados)) to get a copy-pasteable version) and your full plot code—this will help narrow down the exact issue.

内容的提问来源于stack exchange，提问作者Diego Pacheco