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’.