Radar chart with several individuals



It is possible to display several groups on the same radar chart. This post describes how to draw it with R and the fmsb library.

Radar section Warning

Multi-group spider chart, no options


If you’re using the fmsb package for the first time, have a look to the most basic radar chart first, it explains how the data must be formatted for the radarchart() function.

If you have several individuals, the code looks pretty much the same as shown below.

Note: don’t show more that 2 or 3 groups on the same web chart, it would make it unreadable. Read more about radar chart caveats.

# Library
library(fmsb)
 
# Create data: note in High school for several students
set.seed(99)
data <- as.data.frame(matrix( sample( 0:20 , 15 , replace=F) , ncol=5))
colnames(data) <- c("math" , "english" , "biology" , "music" , "R-coding" )
rownames(data) <- paste("mister" , letters[1:3] , sep="-")
 
# To use the fmsb package, I have to add 2 lines to the dataframe: the max and min of each variable to show on the plot!
data <- rbind(rep(20,5) , rep(0,5) , data)
 
# plot with default options:
radarchart(data)

Customization


The radarchart() function offers several options to customize the chart:

  • Polygon features:
    • pcol → line color
    • pfcol → fill color
    • plwd → line width

  • Grid features:
    • cglcol → color of the net
    • cglty → net line type (see possibilities)
    • axislabcol → color of axis labels
    • caxislabels → vector of axis labels to display
    • cglwd → net width

  • Labels:
    • vlcex → group labels size

# Library
library(fmsb)
 
# Create data: note in High school for several students
set.seed(99)
data <- as.data.frame(matrix( sample( 0:20 , 15 , replace=F) , ncol=5))
colnames(data) <- c("math" , "english" , "biology" , "music" , "R-coding" )
rownames(data) <- paste("mister" , letters[1:3] , sep="-")
 
# To use the fmsb package, I have to add 2 lines to the dataframe: the max and min of each variable to show on the plot!
data <- rbind(rep(20,5) , rep(0,5) , data)

# Color vector
colors_border=c( rgb(0.2,0.5,0.5,0.9), rgb(0.8,0.2,0.5,0.9) , rgb(0.7,0.5,0.1,0.9) )
colors_in=c( rgb(0.2,0.5,0.5,0.4), rgb(0.8,0.2,0.5,0.4) , rgb(0.7,0.5,0.1,0.4) )

# plot with default options:
radarchart( data  , axistype=1 , 
    #custom polygon
    pcol=colors_border , pfcol=colors_in , plwd=4 , plty=1,
    #custom the grid
    cglcol="grey", cglty=1, axislabcol="grey", caxislabels=seq(0,20,5), cglwd=0.8,
    #custom labels
    vlcex=0.8 
    )

# Add a legend
legend(x=0.7, y=1, legend = rownames(data[-c(1,2),]), bty = "n", pch=20 , col=colors_in , text.col = "grey", cex=1.2, pt.cex=3)

About axis limits


In the previous examples, axis limits were set in the 2 first rows of the input dataset.

If you do not specify these values, the axis limits will be computed automatically, as shown below.

# Library
library(fmsb)
 
# Create data: note in High school for several students
set.seed(99)
data <- as.data.frame(matrix( sample( 0:20 , 15 , replace=F) , ncol=5))
colnames(data) <- c("math" , "english" , "biology" , "music" , "R-coding" )
rownames(data) <- paste("mister" , letters[1:3] , sep="-")
 
# To use the fmsb package, I have to add 2 lines to the dataframe: the max and min of each variable to show on the plot!
data <- rbind(rep(20,5) , rep(0,5) , data)
 
# Set graphic colors
library(RColorBrewer)
coul <- brewer.pal(3, "BuPu")
colors_border <- coul
library(scales)
colors_in <- alpha(coul,0.3)

# If you remove the 2 first lines, the function compute the max and min of each variable with the available data:
radarchart( data[-c(1,2),]  , axistype=0 , maxmin=F,
    #custom polygon
    pcol=colors_border , pfcol=colors_in , plwd=4 , plty=1,
    #custom the grid
    cglcol="grey", cglty=1, axislabcol="black", cglwd=0.8, 
    #custom labels
    vlcex=0.8 
    )

# Add a legend
legend(x=0.7, y=1, legend = rownames(data[-c(1,2),]), bty = "n", pch=20 , col=colors_in , text.col = "grey", cex=1.2, pt.cex=3)

Warning


There is a lot of criticism going around spider chart. Before using it in a project, you probably want to learn more about it.

Why it’s dangerous Radar chart section

Related chart types


Barplot
Spider / Radar
Wordcloud
Parallel
Lollipop
Circular Barplot



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