Documentation for uniqueN is misleading

[SymbolixAU]

from ?uniqueN

uniqueN is equivalent to length(unique(x)) but much faster. It accepts atomic vectors, data.frames and data.tables. The number of unique rows are computed directly without materialising the intermediate unique data.table and is therefore memory efficient as well.

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uniqueN is not equivalent to length(unique(x)) when x is a data.frame or data.table. Perhaps it should read something like:

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uniqueN is equivalent to length(unique(x)) when x is a vector, and nrow(unique(x)) when x is a data.frame or data.table. The number of unique rows are computed directly without materialising the intermediate unique data.table and is therefore faster and more memory efficient.