# 84 Tutorial of radar chart

Pengyu Zou and Nuanyu Shou

## 84.1 Overview

Radar chart is a useful chart to display multivariate observations with an arbitrary number of variables. It consists of a sequence of equi-angular spokes, called radii, with each spoke representing one of the variables. The data length of a spoke is proportional to the magnitude of the variable for the data point relative to the maximum magnitude of the variable across all data points. Radar charts are widely used in sports to chart players’ strengths and weaknesses.

In this document, we will introduce how to draw a radar charts using package ggradar and fmsb. For each method, we will give instructions about installation, simple example and parameter usage tutorial. Besides, we explore how to use plotly to make the radar chart more readable and interactive.

### 84.2.1 Installation

#### 84.2.1.1 Install by devtools

##### 84.2.1.1.1ggradar is a github package and requires devtools to install it. Run following script to install ggradar.
devtools::install_github("ricardo-bion/ggradar",dependencies = TRUE,force = T")

#### 84.2.1.2 Unzip package in the R directory

##### 84.2.1.2.3 Step3: Open terminal(Mac) or Command(Windows) in this directory and run the following script.
Rcmd build ggradar-master

##### 84.2.1.2.5 Step4:Install ggradar in RStudio

Open the RStudio, Tools -> Install Package and choose install from Package Archive File(.zip; .tar.gz).

### 84.2.2 Simple Example

ggradar takes the first string column as group name and the rest numeric columns as different axes to plot. We take the columns from 6 to 10 in the mtcars dataset, and the first column as Group name.

#load data
as_tibble(rownames = "group") %>%
mutate_at(vars(-group), rescale) %>%
tail(2) %>%
select(1,6:10)

#check data type with std() function
str(mtcars_radar)
## tibble [2 × 6] (S3: tbl_df/tbl/data.frame)
##  $group: chr [1:2] "Maserati Bora" "Volvo 142E" ##$ drat : num [1:2] 0.359 0.622
##  $wt : num [1:2] 0.526 0.324 ##$ qsec : num [1:2] 0.0119 0.4881
##  $vs : num [1:2] 0 1 ##$ am   : num [1:2] 1 1
ggradar(mtcars_radar)

We can find that there are three circle lines in this radar chart, which stand for three bar values. Here are 0%, 50% and 100%. In addition, there are five axes corresponding to the five columns in the data. Each axis is connected with the inner layer with a solid line.

### 84.2.3 Parameters Usage

#### 84.2.3.1 Change text size

axis.label.size is for the axis text.

ggradar(mtcars_radar,axis.label.size = 10)

grid.label.size is for the text of three grids.

ggradar(mtcars_radar,grid.label.size = 10)

#### 84.2.3.2 Set the bar value for each grid

values.radar is for setting the value for each grid. It only takes three values. If provide more than three, only the first three will be taken.

ggradar(mtcars_radar,
# "125%" will be ignore.
)

#### 84.2.3.3 Set the split ratio for each grid

Three grids will split data by ratio according to grid.max, grid.mid and grid.min. This should be correspond to values.radar.

ggradar(mtcars_radar,
grid.max = 1,
grid.mid = 0.6,
grid.min = 0
)

#### 84.2.3.4 Legend

If you want to get rid of the legend you can set plot.legend = FALSE or legend.position = "none.

ggradar(mtcars_radar,
plot.legend = FALSE)
ggradar(mtcars_radar,
legend.position = "none")

#### 84.2.3.5 Background and styles of grid lines.

Use background.circle.colour to set the background color of the chart. gridline.max.colour, gridline.min.colour and gridline.max.colour are for the colors of three grid lines. gridline.min.linetype can set style of grid line to solid or longdash.

ggradar(mtcars_radar,
background.circle.colour = 'yellow',
gridline.min.colour = 'red',
gridline.mid.colour = 'blue',
gridline.max.colour = 'green',
gridline.min.linetype = 'solid')

#### 84.2.3.6 Set the colors of axes.

group.colours take a c() of colors for each group.

ggradar(mtcars_radar,
group.colours = c('red','blue'))

#### 84.2.3.7 Set the size of point

group.point.size only take one value or values of the data size.

ggradar(mtcars_radar,
group.point.size = 8
)
ggradar(mtcars_radar,
group.point.size = c(rep(2,6),rep(12, 6))
)

#### 84.2.3.8 Set the width of line

group.line.width only take one value or values of the data size.

ggradar(mtcars_radar,
group.line.width = 3
)
ggradar(mtcars_radar,
group.line.width = c(rep(1,6),rep(3,6))
)

## 84.3 Radar chart using fmsb

### 84.3.1 Installation

We can install fmsb package using command below:

install.packages("fmsb")

### 84.3.2 Simple Example

By default, data frame must include maximum values as row 1 and minimum values as row 2 for each variables to create axis, and actual data should be given as row 3 and lower rows. So we should first modify the data and use fmsb::radarchart to draw the plot:

df_maxmin <- data.frame(
drat = c(1, 0),
wt = c(1, 0),
qsec = c(1, 0),
vs = c(1, 0),
am = c(1, 0))

fmsb::radarchart(mtcars_radar)

### 84.3.3 Parameters Usage

#### 84.3.3.1 Change the axistype

We can change different axistype

1. 0 – no axis label(Default)

2. 1 – center axis label only

3. 2 – around-the-chart label only

4. 3 – both center and around-the-chart (peripheral) labels

5. 4 – *.** format of axistype1

6. 5 – *.** format of axistype3

par(mar = c(1, 2, 2, 1),mfrow = c(2, 2))
radarchart(mtcars_radar, axistype = 4)

#### 84.3.3.2 Change axis segments

We can modify seg to change the number of segments for each axis. In the plot below, we can see we set the seg = 1 and then segments becomes less.

par(mar = c(1, 1, 2, 1),mfrow = c(1,2))
radarchart(mtcars_radar, axistype = 2, seg = 1)

#### 84.3.3.3 Set Points Symbol

We can modify pty to change point symbol. If you don’t plot data points, it should be 32. And the default value is 16. Besides, there are some other symbol you can try.

par(mar = c(1, 2, 2, 1),mfrow = c(2,2))
radarchart(mtcars_radar, axistype = 2, pty = 18) # square

#### 84.3.3.4 Modify Lines’ Apperance (color/type/width)

1. pcol : A vector of color codes for plot data
2. plty : A vector of line types for plot data
3. plwd : A vector of line widths for plot data
par(mar = c(1, 2, 2, 1),mfrow = c(2,2))
radarchart(mtcars_radar, axistype = 2, plwd = c(0.3,5))

#### 84.3.3.5 Modify the axislines (color/type/width)

We can change axislines appearance using these parameters:

1. cglcol:Line color for radar grids
2. cglty:Line type for radar grids
3. cglwd:Line width for radar grids
par(mar = c(1, 2, 2, 1),mfrow = c(2,2))
radarchart(mtcars_radar, axistype = 2, cglty = 1, cglwd = 3, cglcol = '#000000')

#### 84.3.3.6 Filling Polygons

We can add filling polygons appearance using these parameters:

1. pfcol: A vector of color codes for filling polygons
2. pdensity: A vector of filling density of polygons
3. pangle: A vector of the angles of lines used as filling polygons
par(mar = c(1, 2, 2, 1),mfrow = c(2,2))
radarchart(mtcars_radar, axistype = 2,  pfcol = c(NA,'#99999980'), cglty=1)