datatable.Frame.export_names()

New in version 0.10

Return a tuple of f-expressions for all columns of the frame.

For example, if the frame has columns “A”, “B”, and “C”, then this method will return a tuple of expressions (f.A, f.B, f.C). If you assign these to, say, variables A, B, and C, then you will be able to write column expressions using the column names directly, without using the f symbol:

A, B, C = DT.export_names()
DT[A + B > C, :]

The variables that are “exported” refer to each column by name. This means that you can use the variables even after reordering the columns. In addition, the variables will work not only for the frame they were exported from, but also for any other frame that has columns with the same names.

Parameters

return
Tuple[Expr, ...]

The length of the tuple is equal to the number of columns in the frame. Each element of the tuple is a datatable expression, and can be used primarily with the DT[i,j] notation.

Notes

  • This method is effectively equivalent to:

    def export_names(self):
    return tuple(f[name] for name in self.names)

  • If you want to export only a subset of column names, then you can either subset the frame first, or use *-notation to ignore the names that you do not plan to use:

    A, B = DT[:, :2].export_names()  # export the first two columns
A, B, *_ = DT.export_names()     # same

  • Variables that you use in code do not have to have the same names as the columns:

    Price, Quantity = DT[:, ["sale price", "quant"]].export_names()