codonPython/codonPython/check_null.py at check_null · NHSDigital/codonPython

46 lines (37 loc) · 1.44 KB

import numpy

import pandas as pd

def check_null(dataframe: pd.DataFrame, columns_to_be_checked: list) -> int:

"""

Checks a pandas dataframe for null values

This function takes a pandas dataframe supplied as an argument and returns a integer value representing any null values found within the columns to check

Parameters

----------

data : pandas.DataFrame

Dataframe to read

columns_to_be_checked: list

Given dataframe columns to be checked for null values

Returns

-------

out : int

The number of null values found in the given columns

Examples

--------

>>> check_null(dataframe = pd.DataFrame({'col1': [1,2], 'col2': [3,4]}),columns_to_be_checked = ['col1', 'col2'])

>>> check_null(dataframe = pd.DataFrame({'col1': [1,numpy.nan], 'col2': [3,4]}),columns_to_be_checked = ['col1'])

"""

if not isinstance(columns_to_be_checked, list):

raise ValueError("Please make sure that all your columns passed are strings")

else:

pass

for eachCol in columns_to_be_checked:

if eachCol not in dataframe.columns:

raise KeyError("Please check the column names correspond to values in the DataFrame.")

else:

pass

null_count = 0

for eachColumn in columns_to_be_checked:

prev_null_count = null_count

null_count = prev_null_count + (len(dataframe) - dataframe[eachColumn].count())

return null_count

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