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
C, then you
will be able to write column expressions using the column names
directly, without using the
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.
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.
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()