9.4 Constant Variables
20200814 You may wish and typically do ignore variables (dataset columns) with constant values as they add no extra information to the analysis.
# Identify variables that have a single value. %>% ds select(all_of(vars)) %>% sapply(function(x) all(x == x[1L])) %>% which() %>% names() %T>% print() -> constants
If you are accumulating a list of variables to ignore then add these constants to that list.
# Add to the variables to be ignored for modelling. %<>% union(constants)ignore
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