Trying to have just one legend for many pie charts

Question

[peavy]

Hey my code is below. Im trying to just create one legend for several graphs generated.

dvac = read.csv("2023 dvac.csv")
dvacbar = dvac[, c(1:5, 7:23),]
# Replace N/A values with 0 in columns starting with "Value"
dvacbar <- dvacbar %>%
  mutate_all(~replace_na(., 0))

# Calculate the total abundance for each site and sample
siteSampleTotalAbundance <- dvacbar %>%
  group_by(Site, Sample) %>%
  summarise(TotalAbundance = sum(across(starts_with("Value")), na.rm = TRUE))

# Merge the total abundance back to the original data
dvacbar <- left_join(dvacbar, siteSampleTotalAbundance, by = c("Site", "Sample"))

DCDvac <- filter(dvacbar, Irrigation == "Dryland", Tillage == "Conventional")
DC=DCDvac[, c(1,5, 6:23),]

DC <- DC %>%
  group_by(Site, Sample) %>%
  mutate_at(vars(starts_with("Value")), ~ (. / sum(.)) * 100)

# Melt the data to long format
DCLong <- melt(DC, id.vars = c("Site", "Sample"), variable.name = "Variable")

# Create a list to store individual pie charts
pie_charts <- list()

# Loop through each unique combination of Site and Sample
for (site in unique(DCLong$Site)) {
  for (sample in unique(DCLong$Sample)) {
    # Subset data for the current Site and Sample
    subset_data <- filter(DCLong, Site == site, Sample == sample)

    # Create pie chart for the subset
    pie_chart <- ggplot(subset_data, aes(x = "", y = value, fill = Variable)) +
      geom_bar(stat = "identity", width = 1) +
      coord_polar("y", start = 0) +
      theme_void() +
      labs(fill = "Variable") +
      ggtitle(paste("Percentage of Abundance by Variable at", site, "-", sample)) +
      theme(plot.title = element_text(hjust = 0.5)) 


    # Append the pie chart to the list
    pie_charts[[paste(site, sample, sep = "_")]] <- pie_chart
  }
}

# Display the individual pie charts
gridExtra::grid.arrange(grobs = pie_charts, ncol = 3)

[Trivas]

Is there a reason you can't use facet_wrap with pie charts?

[peavy]

it probably does work. Im currently troubleshooting this error Error in draw_panels(): ! facet_wrap() can't use free scales with coord_polar()

[Trivas]

You would have to restructure your input dataframe to long format and do facet_wrap(Site ~ Sample) rather than using nested loops to subset your dataframe.