statsmodels.tools.tools.add_constant¶

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

Add a column of ones to an array.

Parameters:¶

data : array_like¶

A 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 any column has a constant value. Using ‘add’ will add a column of 1s if a constant column is present.

Returns:¶

The original values with a constant (column of ones) as the first or last column. Returned value type depends on input type.

Return type:¶

array_like

Notes

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