Closing the lines in a ggplot2 radar / spider chart - r

Question

I need a flexible way to make radar / spider charts in ggplot2. From solutions I've found on github and the ggplot2 group, I've come this far:
library(ggplot2)
# Define a new coordinate system
coord_radar <- function(...) {
structure(coord_polar(...), class = c("radar", "polar", "coord"))
}
is.linear.radar <- function(coord) TRUE
# rescale all variables to lie between 0 and 1
scaled <- as.data.frame(lapply(mtcars, ggplot2:::rescale01))
scaled$model <- rownames(mtcars) # add model names as a variable
as.data.frame(melt(scaled,id.vars="model")) -> mtcarsm
ggplot(mtcarsm, aes(x = variable, y = value)) +
geom_path(aes(group = model)) +
coord_radar() + facet_wrap(~ model,ncol=4) +
theme(strip.text.x = element_text(size = rel(0.8)),
axis.text.x = element_text(size = rel(0.8)))
which works, except for the fact that lines are not closed.
I thougth that I would be able to do this:
mtcarsm <- rbind(mtcarsm,subset(mtcarsm,variable == names(scaled)[1]))
ggplot(mtcarsm, aes(x = variable, y = value)) +
geom_path(aes(group = model)) +
coord_radar() + facet_wrap(~ model,ncol=4) +
theme(strip.text.x = element_text(size = rel(0.8)),
axis.text.x = element_text(size = rel(0.8)))
in order to join the lines, but this does not work. Neither does this:
closes <- subset(mtcarsm,variable == names(scaled)[c(1,11)])
ggplot(mtcarsm, aes(x = variable, y = value)) +
geom_path(aes(group = model)) +
coord_radar() + facet_wrap(~ model,ncol=4) +
theme(strip.text.x = element_text(size = rel(0.8)),
axis.text.x = element_text(size = rel(0.8))) + geom_path(data=closes)
which does not solve the problem, and also produces lots of
"geom_path: Each group consist of only one observation. Do you need to
adjust the group aesthetic?"
messages. Som, how do I go about closing the lines?
/Fredrik

Answer 1

Using the new ggproto mechanism available in ggplot2 2.0.0, coord_radar can be defined as:
coord_radar <- function (theta = "x", start = 0, direction = 1)
{
theta <- match.arg(theta, c("x", "y"))
r <- if (theta == "x")
"y"
else "x"
ggproto("CoordRadar", CoordPolar, theta = theta, r = r, start = start,
direction = sign(direction),
is_linear = function(coord) TRUE)
}
Not sure if the syntax is perfect but it is working...

Answer 2

The codes here seem outdated for ggplot2: 2.0.0
Try my package zmisc: devtools:install_github("jerryzhujian9/ezmisc")
After you install it, you will be able to run:
df = mtcars
df$model = rownames(mtcars)
ez.radarmap(df, "model", stats="mean", lwd=1, angle=0, fontsize=0.6, facet=T, facetfontsize=1, color=id, linetype=NULL)
ez.radarmap(df, "model", stats="none", lwd=1, angle=0, fontsize=1.5, facet=F, facetfontsize=1, color=id, linetype=NULL)
if you are curious about what's inside, see my codes at github:
The main codes were adapted from http://www.cmap.polytechnique.fr/~lepennec/R/Radar/RadarAndParallelPlots.html

Answer 3

solution key factor
add duplicated mpg row after melt by rbind
inherit CoordPolar on ggproto
set is_linear = function() TRUE on ggproto
especially is_linear = function() TRUE is important,
since if not you will get plot like this...
with is_linear = function() TRUE settings you can get,
library(dplyr)
library(data.table)
library(ggplot2)
rm(list=ls())
scale_zero_to_one <-
function(x) {
r <- range(x, na.rm = TRUE)
min <- r[1]
max <- r[2]
(x - min) / (max - min)
}
scaled.data <-
mtcars %>%
lapply(scale_zero_to_one) %>%
as.data.frame %>%
mutate(car.name=rownames(mtcars))
plot.data <-
scaled.data %>%
melt(id.vars='car.name') %>%
rbind(subset(., variable == names(scaled.data)[1]))
# create new coord : inherit coord_polar
coord_radar <-
function(theta='x', start=0, direction=1){
# input parameter sanity check
match.arg(theta, c('x','y'))
ggproto(
NULL, CoordPolar,
theta=theta, r=ifelse(theta=='x','y','x'),
start=start, direction=sign(direction),
is_linear=function() TRUE)
}
plot.data %>%
ggplot(aes(x=variable, y=value, group=car.name, colour=car.name)) +
geom_path() +
geom_point(size=rel(0.9)) +
coord_radar() +
facet_wrap(~ car.name, nrow=4) +
theme_bw() +
theme(
axis.title.y = element_blank(),
axis.text.y = element_blank(),
axis.ticks.y = element_blank(),
axis.title.x = element_blank(),
legend.position = 'none') +
labs(title = "Cars' Status")
final result

Answer 4

Sorry, I was beeing stupid. This seems to work:
library(ggplot2)
# Define a new coordinate system
coord_radar <- function(...) {
structure(coord_polar(...), class = c("radar", "polar", "coord"))
}
is.linear.radar <- function(coord) TRUE
# rescale all variables to lie between 0 and 1
scaled <- as.data.frame(lapply(mtcars, ggplot2:::rescale01))
scaled$model <- rownames(mtcars) # add model names as a variable
as.data.frame(melt(scaled,id.vars="model")) -> mtcarsm
mtcarsm <- rbind(mtcarsm,subset(mtcarsm,variable == names(scaled)[1]))
ggplot(mtcarsm, aes(x = variable, y = value)) +
geom_path(aes(group = model)) +
coord_radar() + facet_wrap(~ model,ncol=4) +
theme(strip.text.x = element_text(size = rel(0.8)),
axis.text.x = element_text(size = rel(0.8)))

Answer 5

It turns out than geom_polygom still produces a polygon in the polar coordinates so that
# rescale all variables to lie between 0 and 1
scaled <- as.data.frame(lapply(mtcars, ggplot2:::rescale01))
scaled$model <- rownames(mtcars) # add model names as a variable
# melt the dataframe
mtcarsm <- reshape2::melt(scaled)
# plot it as using the polygon geometry in the polar coordinates
ggplot(mtcarsm, aes(x = variable, y = value)) +
geom_polygon(aes(group = model), color = "black", fill = NA, size = 1) +
coord_polar() + facet_wrap( ~ model) +
theme(strip.text.x = element_text(size = rel(0.8)),
axis.text.x = element_text(size = rel(0.8)),
axis.ticks.y = element_blank(),
axis.text.y = element_blank()) +
xlab("") + ylab("")
works perfectly...

Answer 6

Thank you guys for the help but it did not cover all of my needs. I used two series of data to be compared so I took the subset of mtcars for Mazda:
nobody mentioned about order of the x variable and ggplot2 sorts this variable for the plot but does not sort the data and it made my chart wrong at the first attempt. Apply sorting function for me it was dplyr::arrange(plot.data, x.variable.name)
I needed to annotate the chart with values and ggplot2::annotate() works fine but it was not included in the recent answers
the above code did not work fine for my data until adding ggplot2::geom_line
Finally this code chunk did my chart:
scaled <- as.data.frame(lapply(mtcars, ggplot2:::rescale01))
scaled$model <- rownames(mtcars)
mtcarsm <- scaled %>%
filter(grepl('Mazda', model)) %>%
gather(variable, value, mpg:carb) %>%
arrange(variable)
ggplot(mtcarsm, aes(x = variable, y = value)) +
geom_polygon(aes(group = model, color = model), fill = NA, size = 1) +
geom_line(aes(group = model, color = model), size = 1) +
annotate("text", x = mtcarsm$variable, y = (mtcarsm$value + 0.05), label = round(mtcarsm$value, 2), size = 3) +
theme(strip.text.x = element_text(size = rel(0.8)),
axis.text.x = element_text(size = rel(1.2)),
axis.ticks.y = element_blank(),
axis.text.y = element_blank()) +
xlab("") + ylab("") +
guides(color = guide_legend()) +
coord_radar()
Hopefully usefull for somebody