One-of-N codes

All the preceding discussion has concerned continuous numerical data. Not all data is of this form, and we now discuss the encoding of nonnumerical data. Logical variables have one of two values that are encoded as zero and one. An example is the presence or absence (a yes or no) of a feature. Typically the presence (yes) is encoded as a 1 and the absence (no) as a 0. Categorical data should be encoded in some variation of a one-of-N code (N equals the number of categories) or a thermometer code. 

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