Product Code Database
| 00000001 |
| 00000010 |
| 00000100 |
| 00001000 |
| 00010000 |
| 00100000 |
| 01000000 |
| 10000000 |
In digital circuits and machine learning, a one-hot is a group of Bit among which the legal combinations of values are only those with a single high (1) bit and all the others low (0). A similar implementation in which all bits are '1' except one '0' is sometimes called one-cold. In statistics, dummy variables represent a similar technique for representing categorical data.
A ring counter with 15 sequentially ordered states is an example of a state machine. A 'one-hot' implementation would have 15 flip-flops chained in series with the Q output of each flip-flop connected to the D input of the next and the D input of the first flip-flop connected to the Q output of the 15th flip-flop. The first flip-flop in the chain represents the first state, the second represents the second state, and so on to the 15th flip-flop, which represents the last state. Upon reset of the state machine all of the flip-flops are reset to '0' except the first in the chain, which is set to '1'. The next clock edge arriving at the flip-flops advances the one 'hot' bit to the second flip-flop. The 'hot' bit advances in this way until the 15th state, after which the state machine returns to the first state.
An address decoder converts from binary to one-hot representation. A priority encoder converts from one-hot representation to binary.
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| +Label Encoding !Food Name !Categorical # !Calories | ||
| Apple | 1 | 95 |
| Chicken | 2 | 231 |
| Broccoli | 3 | 50 |
| +One-Hot Encoding !Apple !Chicken !Broccoli !Calories | |||
| 1 | 0 | 0 | 95 |
| 0 | 1 | 0 | 231 |
| 0 | 0 | 1 | 50 |
Categorical data can be either Nominal number or Ordinal number.Stevens, S. S. (1946). “On the Theory of Scales of Measurement”. Science, New Series, 103.2684, pp. 677–680. http://www.jstor.org/stable/1671815. Ordinal data has a ranked order for its values and can therefore be converted to numerical data through ordinal encoding.Brownlee, Jason. (2020). "Ordinal and One-Hot Encodings for Categorical Data"
For each unique value in the original categorical column, a new column is created in this method. These dummy variables are then filled up with zeros and ones (1 meaning TRUE, 0 meaning FALSE).
Because this process creates multiple new variables, it is prone to creating a 'big p' problem (too many predictors) if there are many unique values in the original column. Another downside of one-hot encoding is that it causes multicollinearity between the individual variables, which potentially reduces the model's accuracy.
Also, if the categorical variable is an output variable, you may want to convert the values back into a categorical form in order to present them in your application.Brownlee, Jason. (2017). "Why One-Hot Encode Data in Machine Learning?"
/ref> An example of ordinal data would be the ratings on a test ranging from A to F, which could be ranked using numbers from 6 to 1. Since there is no quantitative relationship between nominal variables' individual values, using ordinal encoding can potentially create a fictional ordinal relationship in the data.Brownlee, Jason. (2020). "Ordinal and One-Hot Encodings for Categorical Data"
/ref> Therefore, one-hot encoding is often applied to nominal variables, in order to improve the performance of the algorithm.
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See also
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