Bar Chart of One Variable
One of the most frequently encountered visualizations is the bar chart, created for a categorical variable.
Bar chart: Plot a number associated with each category of a categorical variable as the height of the corresponding bars.
A call to a function to create a bar chart contains the name of the variable that contains the categories to be plotted. With the BarChart() function, that variable name is the first argument passed to the function. In this example, the only argument passed to the function is the variable name as the data frame is named d, the default value. The following illustrates the call to BarChart() with a categorical variable named \(x\).
When only a single categorical variable is passed to BarChart(), the numerical value associated with each bar is the corresponding count of the number of occurrences, automatically computed.
Default Bar Chart
Consider the categorical variable Dept in the Employee data table. Use BarChart() to tabulate and display the visualization of the number of employees in each department, here relying upon the default data frame (table) named d. Otherwise add the data= option if the data frame has another name.
Bar chart of tablulated counts of employees in each department.
## >>> Suggestions
## BarChart(Dept, horiz=TRUE) # horizontal bar chart
## BarChart(Dept, fill="greens") # sequential green bars
## PieChart(Dept) # doughnut (ring) chart
## Plot(Dept) # bubble plot
## Plot(Dept, stat="count") # lollipop plot
##
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## --- Dept ---
##
##
## Missing Values of Dept: 1
##
##
## ACCT ADMN FINC MKTG SALE Total
## Frequencies: 5 6 4 6 15 36
## Proportions: 0.139 0.167 0.111 0.167 0.417 1.000
##
##
## Chi-squared test of null hypothesis of equal probabilities
## Chisq = 10.944, df = 4, p-value = 0.027The default color theme, "colors", fills the bars in the bar chart with with different hues. See more explanation of this and related color palettes more in the vignette Customize.
The BarChart() function also labels each bar with the associated numerical value. The function also provides the corresponding frequency distribution, the table that lists the count of each category, from which the bar chart is constructed.
We do not need to see this output to the R console repeated again for different bar charts of the same data, so turn off for now with the parameter quiet set to TRUE. Can set this option for each call to BarChart(), or can set for subsequent analyses with the style() function.
Custom Colors
Specify a single fill color with the fill parameter, the edge color of the bars with color, and a horizontal bar chart with base R parameter horiz. Turn off console output. Turn off the displayed value on each bar with the parameter values set to off.
Use the theme parameter to change the entire color theme: “colors”, “lightbronze”, “dodgerblue”, “darkred”, “gray”, “gold”, “darkgreen”, “blue”, “red”, “rose”, “green”, “purple”, “sienna”, “brown”, “orange”, “white”, and “light”. In this example, changing the full theme accomplishes th same as changing the fill color.
Or, can use style() to change the theme for subsequent visualizations as well. See the Customize vignette.
Dept is not an ordinal variable (i.e., with ordered values), but to illustrate, can choose many different sequential palettes from getColors(): “reds”, “rusts”, “browns”, “olives”, “greens”, “emeralds”, “turquoises”, “aquas”, “blues”, “purples”, “violets”, “magentas”, and “grays”.
Long Value Labels
Rotate and offset the axis labels with rotate_x and offset parameters. Do a descending sort of the categories by frequencies with the sort parameter.
Instead of setting the value of the interior color of the bars with the fill parameter, map the value of tabulated count to bar fill. With mapping, the color of the bars reflects the bar height. The higher the bar, the darker the color.
Specify the Numerical Variable
One possibility is to have the values of the \(x\) and \(y\) variables, such as in a table, and want to create the bar chart directly from the table. To do so, enter the paired data values into a data file such as with Excel, and then read into R with Read() When calling BarChart(), specify first the categorical \(x\) variable and then the numerical \(y\) variable. The general syntax follows.
Can also do a statistical transformation of \(y\). Set the bars proportional to the height of the corresponding mean deviations of \(y\) with the stat parameter. Possible values of stat: "sum",“mean”,“sd”,“dev”,“min”,“median”, and“max”. The“dev”` value displays the mean deviations to further facilitate a comparison among levels.
Here the \(x\)-variable is Dept and \(y\)-variable is Salary. Display bars for values of dev <= 0 in a different color than values above with the fill_split parameter set at 0. Do an ascending sort with the sort parameter set at "+".
Annotation
Annotate a plot with the add parameter. To add a rectangle use the "rect" value of add. Here set the rectangle around the message centered at <3,10>. To specify a rectangle requires two corners of the rectangle, <x1,y1> and <x2,y2>. To specify text requires just a single coordinate, <x1,y1>. Because with the add parameter, the message follows the specification of "rect", the coordinates of the text message follows the coordinates for the rectangle.
First lighten the fill color of the annotation with the add_fill parameter for the style() function.
style(add_fill="aliceblue")
BarChart(Dept, add=c("rect", "Employees by\nDepartment"),
x1=c(1.75,3), y1=c(11, 10), x2=4.25, y2=9)
