DataFrame colon : vs bang ! indexing

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From DataFrames.jl’s documentation:

https://dataframes.juliadata.org/stable/man/getting_started/

Columns can be directly (i.e. without copying) extracted using df.col, df."col", df[!, :col] or df[!, "col"] (this rule applies to getting data from a data frame, not writing data to a data frame). The two latter syntaxes are more flexible as they allow passing a variable holding the name of the column, and not only a literal name. Note that column names can be either symbols (written as :col, :var"col" or Symbol("col")) or strings (written as "col"). In the forms df."col" and :var"col" variable interpolation into a string using $ does not work. Columns can also be extracted using an integer index specifying their position.

Since df[!, :col] does not make a copy, changing the elements of the column vector returned by this syntax will affect the values stored in the original df. To get a copy of the column use df[:, :col]: changing the vector returned by this syntax does not change df.

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