tools.tools.add_constant()

statsmodels.tools.tools.add_constant

statsmodels.tools.tools.add_constant(data, prepend=True, has_constant='skip') [source]

Adds a column of ones to an array

Parameters:

data : array-like data is the column-ordered design matrix prepend : bool If true, the constant is in the first column. Else the constant is appended (last column). has_constant : str {‘raise’, ‘add’, ‘skip’} Behavior if data already has a constant. The default will return data without adding another constant. If ‘raise’, will raise an error if a constant is present. Using ‘add’ will duplicate the constant, if one is present.

Returns:

data : array, recarray or DataFrame The original values with a constant (column of ones) as the first or last column. Returned value depends on input type.

Notes

When the input is recarray or a pandas Series or DataFrame, the added column’s name is ‘const’.