MATLAB Fundamentals＞＞Representing Discrete Categories

MATLAB Fundamentals>Specialized Data Types>Representing Discrete Categories>(1/6) Introduction

Representing Discrete Categories

When text labels are intended to represent a finite set of possibilities, a string array may use more memory than a?categorical?array. There are functions designed to work with categories of data, so if your text describes a group or category, this is often the best data type.
当文本标签旨在表示一组有限的可能性时，字符串数组可能比分类数组使用更多的内存。有些函数是为处理数据类别而设计的，因此，如果您的文本描述了一个组或类别，这通常是最好的数据类型。

MATLAB Fundamentals>Specialized Data Types>Representing Discrete Categories>(2/6) Converting to and Operating on Categoricals

This code sets up the activity.

x = ["C","B","C","A","B","A","C"]

This line of code would produce an error.

% histogram(x)

说明1：You can convert a string array to a categorical using the?categorical?function.

任务1：Convert?x?into a categorical array named?y.

解答：

y = categorical(x)

说明2：Categorical arrays take up less memory than cell arrays of strings.

任务2：Issue the?whos?x?y?command to see how much memory each variable uses.

解答：

whos x y

任务3：

You can see the categories represented in a categorical array using the?categories?function on the categorical array.

解答：

cats = categories(y)

任务4：

Create a variable named?iC?which contains values of?true?corresponding to the values in?y?that equal?C.

解答：

iC = y == "C"

任务5：

Create a variable named?iNB?which contains values of?true?corresponding to the values in?y?that are not equal to?B.

解答：

iNB = y ~= "B"

附加练习：Try indexing into?y?with?iC?and?iNB.

解答：

iCidx = y(iC)
iNBidx = y(iNB)

笔记：

（1）a string array may use more memory than a?categorical?array字符串数组比分类数组占用更多内存；

（2）任务4和5后面部分可以不使用括号，执行运算顺序为从又向左，即先计算“等于”或“不等于”逻辑，在将结果赋值给左边变量。