ggplot2绘制土壤相关箱线图的技术问题求助

Hi Thiago! Let’s work through your ggplot2 boxplot issue together. First, let me recap the code you shared to make sure I’m aligned with what you’re building:

d.solo <- ggplot(data=dens, aes(x=Textura_do_Solo, y=Densidade))+ 
  geom_boxplot(aes(fill=factor(Tipo_de_Solo)), 
               outlier.color = "black", outlier.shape = 16, outlier.alpha = 1)+ 
  xlab("Soil texture")+ 
  ylab("Wood density (kg/m³)")+ 
  ylim(250,700)+
  # ... your remaining code

Since you didn’t specify the exact problem you’re facing, I’ll walk through the most common pitfalls with this setup and share optimizations to fix or improve your plot:

1. Clean up factor handling #

You’re converting Tipo_de_Solo to a factor inside the aes() call, which works—but handling this upfront in your data makes the code cleaner and avoids repeated conversions:

# Pre-process the factor once
dens$Tipo_de_Solo <- factor(dens$Tipo_de_Solo)

# Now use it directly in ggplot
geom_boxplot(aes(fill=Tipo_de_Solo), ...)

2. Avoid data truncation with ylim() #

Using ylim(250,700) filters out any data points outside this range before calculating boxplot statistics (like quartiles or medians), which can skew your results. Instead, use coord_cartesian() to zoom the axis without modifying your data:

# Replace ylim() with this
coord_cartesian(ylim = c(250, 700))

3. Fix grouping/overlapping boxplots #

If your boxplots for different Tipo_de_Solo values are overlapping under the same Textura_do_Solo category, explicitly set a dodge position to space them out:

geom_boxplot(aes(fill=Tipo_de_Solo),
             outlier.color = "black", outlier.shape = 16, outlier.alpha = 1,
             position = position_dodge(width = 0.8)) # Adjust width as needed

4. Polish labels and legend #

Make your plot more readable by aligning legend labels with your axis text:

# Add this to your ggplot chain
labs(fill = "Soil Type") # Updates the legend title to match your English axis labels

Full Optimized Example Code #

Here’s how all these tweaks come together:

# Pre-process data
dens$Tipo_de_Solo <- factor(dens$Tipo_de_Solo)

# Build the plot
d.solo <- ggplot(data=dens, aes(x=Textura_do_Solo, y=Densidade))+ 
  geom_boxplot(aes(fill=Tipo_de_Solo),
               outlier.color = "black", outlier.shape = 16, outlier.alpha = 1,
               position = position_dodge(width = 0.8))+ 
  xlab("Soil texture")+ 
  ylab("Wood density (kg/m³)")+ 
  coord_cartesian(ylim = c(250, 700))+
  labs(fill = "Soil Type")+
  theme_minimal() # Optional: Clean up the plot theme

If you’re dealing with a specific issue (like missing data, broken legends, or error messages), share those details and I’ll help you troubleshoot further!

内容的提问来源于stack exchange，提问作者T. W.G. de Oliveira