densityBy: Create a 'violin plot' or density plot of the distribution of...

In psych: Procedures for Psychological, Psychometric, and Personality Research

Create a 'violin plot' or density plot of the distribution of a set of variables

Description

Among the many ways to describe a data set, one is a density plot for each value of a grouping variable and another is violin plot of multiple variables. A density plot shows the density for different groups to show effect sizes. A violin plot is similar to a box plot but shows the actual distribution. Median and 25th and 75th percentile lines are added to the display. If a grouping variable is specified, violinBy will draw violin plots for each variable and for each group. Data points may be drawn as well in what is known as a "raincloud plot".

Usage

violin(x,data=NULL, var=NULL, grp=NULL, grp.name=NULL, xlab=NULL, ylab=NULL,
	main="Density plot", vertical=TRUE, dots=FALSE, rain=FALSE, jitter=.05, alpha=1,
	errors=FALSE, eyes=TRUE, adjust=1, restrict=TRUE, xlim=NULL, add=FALSE, 
	col=NULL, pch=20, scale=NULL,...) 
 
violinBy(x, var=NULL, grp=NULL, data=NULL, grp.name=NULL, xlab=NULL, ylab=NULL,
	main="Density plot", vertical=TRUE, dots=FALSE, rain=FALSE, jitter=.05, alpha= 1,
	errors=FALSE, eyes=TRUE, adjust=1, restrict=TRUE, xlim=NULL, add=FALSE, 
	col=NULL, pch=20, scale=NULL,...) 
 
densityBy(x, var=NULL, grp=NULL,data=NULL, freq=FALSE, col=c("blue","red","black"), 
	alpha=.5, adjust=1, ylim=NULL, xlim=NULL, xlab="Variable", ylab="Density",
     main="Density Plot",legend=NULL)

Arguments

x	A matrix or data.frame (can be expressed in formula input)
var	The variable(s) to display
grp	The grouping variable(s)
data	The name of the data object if using formula input
grp.name	If the grouping variable is specified, then what names should be give to the group? Defaults to 1:ngrp
ylab	The y label
xlab	The x label
main	Figure title
vertical	If TRUE, plot the violins vertically, otherwise, horizontonally
dots	if TRUE, add a stripchart with the data points
rain	If TRUE, draw a half violin with rain drops
jitter	If doing a stripchart, then jitter the points this much
errors	If TRUE, add error bars or cats eyes to the violins
eyes	if TRUE and errors=TRUE, then draw cats eyes
alpha	A degree of transparency (0=transparent ... 1 not transparent)
adjust	Allows smoothing of density histograms when plotting variables like height
freq	if TRUE, then plot frequencies (n * density)
restrict	Restrict the density to the observed max and min of the data
xlim	if not specified, will be .5 beyond the number of variables
ylim	If not specified, determined by the data
add	Allows overplotting
col	Allows for specification of colours. The default for 2 groups is blue and red, for more group levels, rainbows.
pch	The plot character for the mean is by default a small filled circle. To not show the mean, use pch=NA
scale	If NULL, scale the widths by the square root of sample size, otherwise scale by the value supplied.
legend	If not NULL, draw a legend at c(topleft,topright,top,left,right)
...	Other graphic parameters

Details

Describe the data using a violin plot. Change alpha to modify the shading. The grp variable may be used to draw separate violin plots for each of multiple groups.

For relatively smallish data sets (< 500-1000), it is informative to also show the actual data points. This done with the dots=TRUE option. The jitter value is arbitrarily set to .05, but making it larger (say .1 or .2) will display more points.

Perhaps even prettier, is draw "raincloud" plots (half violins with rain drops)

Value

The density (y axis) by value (x axis) of the data (for densityBy) or a violin plot for each variable (perhaps broken down by groups)

Note

Formula input added July 12, 2020

Author(s)

William Revelle

See Also

describe, describeBy and statsBy for descriptive statistics and error.bars, error.bars.by and bi.bars, histBy and scatterHist for other graphic displays

Examples

violin(bfi[4:8])
violin(SATV + SATQ ~ gender, data=sat.act, grp.name =cs(MV,FV,MQ,FQ)) #formula input
violinBy(bfi,var=4:7,grp ="gender",grp.name=c("M","F"))
#rain does not work for multiple DVS, just up to 2 IVs 
violinBy(SATV  ~ education,data =sat.act, rain=TRUE, pch=".", vertical=FALSE)  #rain 

densityBy(SATV  ~ gender,data =sat.act,legend=1)  #formula input 

  

psych documentation built on June 27, 2024, 5:07 p.m.