Histograms and Box Plots

Understanding the distribution of data within a column is often essential. Tablesaw provides one and two dimensional histograms, as well as box plots.

The complete code for this example can be found here: https://github.com/tlabs-data/tablesaw/blob/master/jsplot/src/test/java/tech/tablesaw/examples/DistributionVisualizations.java

We start by loading the data we’ll use in our examples below.

Table property = Table.read().csv("sacremento_real_estate_transactions.csv");

Histograms

A one dimensional histogram of property prices is shown below.

Histogram of prices

This plot shows the distribution of injury counts for the most powerful tornadoes. To produce it, we simply filter the table to include only level 5, and call Histogram.create();

Plot.show(Histogram.create("Distribution of prices", property, "price"));

We also take a histogram of sizes, after setting any sizes of 0 square feet to “missing”.

NumberColumn sqft = property.numberColumn("sq__ft");
sqft.set(sqft.isEqualTo(0), DoubleColumnType.missingValueIndicator());

Plot.show(Histogram.create("Distribution of property sizes", property, "sq__ft"));

Histogram of Property sizes

2D Histograms

It may be useful to look at the relationship of two distributions. Ysou can do that with a 2D Histogram.

Plot.show(
    Histogram2D.create("Distribution of price and size", property, "price", "sq__ft"));

aHistogram of price and size

Box plots: Comparing the distributions of sub-groups

Comparing distributions of sub-groups is also really useful. The box plot is ideal for that:

Box plot of price by type

And here’s the code:

Plot.show(BoxPlot.create("Prices by property type", property, "type", "price"));