Programming and Data Types

Organizing Data in Multidimensional Arrays

You can use multidimensional arrays to represent data in two ways:

• As planes or pages of two-dimensional data. You can then treat these pages as matrices.
• As multivariate or multidimensional data. For example, you might have a four-dimensional array where each element corresponds to either a temperature or air pressure measurement taken at one of a set of equally spaced points in a room.

For example, consider an RGB image. For a single image, a multidimensional array is probably the easiest way to store and access data.

To access an entire plane of the image, use

• red_plane = RGB(:,:,1);
  

To access a subimage, use

• subimage = RGB(20:40,50:85,:);
  

The RGB image is a good example of data that needs to be accessed in planes for operations like display or filtering. In other instances, however, the data itself might be multidimensional. For example, consider a set of temperature measurements taken at equally spaced points in a room. Here the location of each value is an integral part of the data set - the physical placement in three-space of each element is an aspect of the information. Such data also lends itself to representation as a multidimensional array.

Now to find the average of all the measurements, use

• mean(mean(mean(TEMP)));
  

To obtain a vector of the "middle" values (element (2,2)) in the room on each page, use

• B = TEMP(2,2,:);
  

Operating on Planes and Matrices

Multidimensional Cell Arrays