densityBy {psych}

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