Slicing, Dicing and Rotating Data

The BIS database on house prices has twelve dimensions, most of which are superfluous; these were reduced using the data import procedures explained later in this tutorial, to leave just four significant dimensions:

Date : Quarterly data from 1927 till 2024 (388 entries)
Unit of Measure
Value
Reference Area : Country or Region (62 entries)

dimension count 4D in the lower right quadrant of the Ravel in Figure 16.

You see the data in a Ravel by attaching a Sheet or Plot to it output port, as shown in Figure 17 to Figure 19.

Figure 18: Output from a Ravel before data selection and axis rotation

The right-pointing axis of the Ravel determines what is shown on the rows of the sheet, while the down-pointing axis determines what is shown by the columns. At present, the displayed axes are Reference Area and Value . The sheet shows a slice of that data for the first entries in the file: Nominal on the Value axis, Index from the Unit of Measure axis, and the first two entries in Reference Area , and the first eight entries from Quarter .

It would be more useful to see the data by Reference Area by Quarter . To get that view, click the left mouse button on the arrowhead of the Quarter axis, hold the button down, and rotate the axis into the down direction, which is currently occupied by the Value axis. When you release the mouse button, the Quarter axis will replace the Unit of measure axis in the down direction, and the data in the Sheet will now have countries by rows and Quarters by columns.

Figure 19: Output from a Ravel after Pivoting the data cube via rotating the axes

The Sheet is still blank, because there is no data for the current selections—the Index for Nominal House Prices in the very first Quarters of the data set (1927 and 1928), for the first few countries in the file (in alphabetical order).

and columns of data (the default setting), which we call the Head, the last few (the Tail), or a few of both (Head and Tail).

Figure 20: Head and Tail selected for Rows and being applied to columns

To show the last few rows of Date data, rotate the Date Axis to where Reference Area is (which will put the dates in the rows and countries in the columns). Then right-click on the Sheet and choose Row Slices/Tail. The sheet will then show the first countries in the data file, and the last quarters.

Figure 21: Output from a Ravel after axis rotation and selecting Head-Tail to display sheet contents

axes. You can control the entry shown using the selector dots on those two axes: these are the coloured dots that are currently within the inner circle of the Ravel. This is called slicing the data.

Selector dots can be moved:

By the mouse. Click on a dot and drag it to the required selection; or
By the arrow keys. Use the mouse to move the cursor so that it is hovering over an axis; then use the up (or right) arrow key to move the dot out towards the arrowhead on an axis, or the down (or left) arrow key to move back towards the center.

To see the Real (CPI-adjusted) annual rate of change of house prices, use the selector dot on those two axes. That selection is shown below—where Date has also been rotated to the rows so that Countries are shown by the columns.

Figure 22: Output from a Ravel after slicing the data using selector dots

Calipers

You can select a contiguous range of data on an axis by inserting a caliper, using the “Toggle axis calipers” item on the context menu for an axis. Calipers initially cover the entire range of the data—see Figure 23.

Figure 23: Calipers applied to a Date axis but not yet calibrated

You then move the ends of its parenthesis to specify where you want the excerpt to begin and end—see Figure 24. If you click on the tip of the parenthesis, you move the entire selection, while maintaining the number of elements it selects on the axis.

Figure 24: Calipers applied and calibrated to data between 2000 and 2012

Future releases of Ravel will support multiple named calipers on an axis, which will enable noncontiguous sets of data to be displayed on the one Sheet or Plot.