import pandas as pd
[docs]def constant_value_imputation(data=None, value=0, columns=None, inplace=False):
"""Fills in missing values with the constant value given. If the data is
passed as a dataframe, the operation can be applied to all columns,
by leaving the parameter columns empty, or to selected columns, passed
as an array of strings.
:param data: The data on which to perform the constant value imputation
:type data: pandas.Series or pandas.DataFrame
:param value: The value with which to fill in missing values. If columns is
not set, the value can be a dict/Series/DataFrame of values specifying
which value to use for each index (for a Series) or column (for a
DataFrame). Values not in the dict/Series/DataFrame will not be filled.
:type value: scalar, dict, Series, or DataFrame, default 0
:param columns: Columns on which to apply the operation.
:type columns: array-like, optional
:param inplace: If True, do operation inplace and return None.
:type inplace: bool, default False
:return: The series or dataframe with NA values filled in, or
None if inplace=True.
:rtype: pandas.Series, pandas.DataFrame, or None
:raises: TypeError, ValueError
"""
# Check if data is a series or dataframe:
if not (isinstance(data, pd.Series) or isinstance(data, pd.DataFrame)):
raise TypeError('The data has to be a Series or DataFrame.')
# Raise a ValueError if columns are selected for a series:
if isinstance(data, pd.Series) and columns is not None:
raise ValueError('Columns can only be selected if the data is a '
'DataFrame.')
# Assign a reference or copy to res, depending on inplace:
if inplace:
res = data
else:
res = data.copy()
if columns is None:
# Treatment for a series or all columns of a dataframe
res.fillna(value=value, inplace=True)
else:
# Treatment for selected columns of a dataframe
for column in columns:
# Raise error if the column name doesn't exist in the data:
if column not in data.columns:
raise ValueError(
'\'' + column + '\' is not a column of the data.'
)
# Fill the missing values of the column
res[column].fillna(value=value, inplace=True)
# Return the imputed data, or None if inplace:
if inplace:
return None
else:
return res