The function "categorical()" can convert continuous data into categorical data. However, this function cannot categorize two numbers if the difference between them is less than 5e-5, i.e., 0.00005. For example, the function does not categorize 1 and 1.00001 into different categories. This behavior is expected and explained well in the categorical document as below.
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If the input array has numeric, datetime, or duration values that are too close together, then the categorical function truncates them to duplicate values. For example, categorical([1 1.00001]) truncates the second element of the input array. To create categories from numeric data, use the discretize function.
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In your example, 0.157132 and 0.157135 are very close to each other and the difference is 3e-6 which is less than 5e-5. Therefore "categorical()" cannot classify the two numbers into two categories. As a workaround, please consider using "discretize()" as below.
categorical(discretize(a, min(a):1e-6:max(a)))
