Make side by side pie-chart for Two different columns in ggplot also facet wrap it for different factors

Question

I am trying to make some pie chart for the data matrix that I have. I have created a dummy matrix below with similar variables. I have two result value to work with that is "AREA" and "EROSION". For each result values I can have one of three factors that is "High Precip Zones", "Moderate Precip. Zones" and "Low Precip. Zones".

I want to show this in piechart of 3 rows and 2 columns. Each row needs to have "Area" pie chart and "Erosion" pie chart for each Zones. I am able to separate the pie chart by adding facet_wrap(~Zones) but I am not sure what I can do to separate the pie chart by two different columns? So that I can show Erosion pie chart and Area pie chart side by side in each row.

Also my original matrix can have upto 15 values in each row which means pie chart is going to be crowded. Is there a way or may be a easy function that I can use the ignore values that are 0 or below certain threshold?

I will appreciate any help and suggestion regarding this.

library(ggplot2)
library(tidyverse)
library(RColorBrewer)
my_pal <- colorRampPalette(brewer.pal(9, "Set1"))

#### create new matrix ############
new_mat<-matrix(, nrow=40, ncol = 4)
colnames(new_mat)<-c("Zones", "ssoilcmb", "Erosion_t", "area..sq.m.")

for ( i in 1:nrow(new_mat)){ 
  new_mat[i,4]<-as.numeric(sample(0:20, 1))
  new_mat[i,3]<-as.numeric(sample(0:20, 1))
  a<-sample(c("S2","S3","S4","S5","S1"),1)
  b<-sample(c("Deep","Moderate","Shallow"),1)
  new_mat[i,1]<-sample(c("High Precip","Moderate Precip","Low Precip"),1)
 
  new_mat[i,2]<-paste0(a,"_",b)
}

m_dt<-as.data.frame(new_mat)
m_dt$Erosion_t<-as.numeric(m_dt$Erosion_t)
m_dt$area..sq.m.<-as.numeric(m_dt$area..sq.m.)

#### calculate parea
m_dt<- m_dt %>%
  group_by(Zones)%>%
  mutate(per_er=signif((`Erosion_t`/sum(`Erosion_t`))*100,3), per_area=signif((`area..sq.m.`/sum(`area..sq.m.`))*100,3))

############ plot 
 ggplot(m_dt, aes(x="", y=per_er, fill=ssoilcmb)) + geom_bar(stat="identity", width=1, position = position_fill())+
  coord_polar("y", start=0) + facet_wrap(~ Zones) +geom_text_repel(aes(label = paste0(per_er, "%")), position = position_fill(vjust = 0.5))+
  scale_fill_manual(values=my_pal(15)) +
  labs(x = NULL, y = NULL, fill = NULL, title = "Erosions")+
  theme_classic() + theme(axis.line = element_blank(),
                          axis.text = element_blank(),
                          axis.ticks = element_blank(),
                          plot.title = element_text(hjust = 0.5, color = "#666666"))

Answer 1

I think you need to rearrange your data in a suitable manner rather than playing with the graphical language itself.

I have given my suggestion here. Please forgive the High, Medium and Low having changed to 1, 2 and 3. I did that to make sense of the data for myself. You will obviously be renaming it.

    library(tidyverse)
library(RColorBrewer)
library(ggrepel)
my_pal <- colorRampPalette(brewer.pal(9, "Set1"))

#### create new matrix ############
new_mat<-matrix(, nrow=40, ncol = 4)
colnames(new_mat)<-c("Zones", "ssoilcmb", "Erosion_t", "area..sq.m.")


for ( i in 1:nrow(new_mat)){ 
  new_mat[i,4]<-as.numeric(sample(0:20, 1))
  new_mat[i,3]<-as.numeric(sample(0:20, 1))
  a<-sample(c("S2","S3","S4","S5","S1"),1)
  b<-sample(c("Deep","Moderate","Shallow"),1)
  new_mat[i,1]<-sample(c("High Precip","Moderate Precip","Low Precip"),1)

  new_mat[i,2]<-paste0(a,"_",b)
}

m_dt<-as.data.frame(new_mat)
m_dt$Erosion_t<-as.numeric(m_dt$Erosion_t)
m_dt$area..sq.m.<-as.numeric(m_dt$area..sq.m.)

#### calculate parea
m_dt<- m_dt %>%
  group_by(Zones)%>%
  mutate(per_er=signif((`Erosion_t`/sum(`Erosion_t`))*100,3), per_area=signif((`area..sq.m.`/sum(`area..sq.m.`))*100,3))

## You must rearrange your data as given here:

a<-data.frame(m_dt$Zones,m_dt$ssoilcmb, m_dt$per_er)
b<-data.frame(m_dt$Zones,m_dt$ssoilcmb, m_dt$per_area)
c<-data.frame(Zones=Zones,ssoilcmb=m_dt$ssoilcmb,
              Parameter=c(rep("Erosion",40),rep("Area",40)),
              Values=c(m_dt$per_er,m_dt$per_area))

### Your New Plot ###

ggplot(c, aes(x="", y=Values, fill=ssoilcmb)) + 
  geom_bar(stat="identity", width=1, position = position_fill())+
  coord_polar("y", start=0) + 
  facet_wrap(Zones~Parameter, nrow = 3) +
  geom_text_repel(aes(label = paste0(Values, "%")), position = position_fill(vjust = 0.5))+
  scale_fill_manual(values=my_pal(15)) +
  labs(x = NULL, y = NULL, fill = NULL, title = "Erosions")+
  theme_classic() + theme(axis.line = element_blank(),
                          axis.text = element_blank(),
                          axis.ticks = element_blank(),
                          plot.title = element_text(hjust = 0.5, color = "#666666"))