The column(x) function may be used only in the using specifier
of a plot, splot, fit, or stats command.
It evaluates to the numerical value of the content of column x.
If the column is expected to hold a string, use instead stringcolumn(x)
or timecolumn(x, "timeformat").
See plot datafile using (p.
), stringcolumn (p.
), timecolumn (p.
).