Analyize cardinalities of a pandas Data.Frame

cardinalities.py

import pandas as pd
import seaborn as sns
def cardinalities(df: pd.DataFrame, plot: bool = False):
    """
    Analyses cardinalities in a data frame

    df DataFrame the data frame to be analyized
    plot Plot whether to plot rather than return the result DataFrame

    returns (DataFrame, Plot) of a matrix M(i,j) that reads row-wise, 
      i.e. for each entry in attribute i, there are 1 (dark) or n (light) values in attribute j
    """

    l = []
    for cnm in df.columns:
        # here is the heart
        # count number of distinct values in any column per value in the grouped column and take max
        rw = df.groupby(cnm).agg(['nunique']).agg(["max"]) > 1
        rw.index = [cnm]
        l += [rw]
    
    car = pd.concat(l)

    # postprocessing
    car = car.sort_index()
    car.columns = df.columns.sort_values()
    car[car == True] = "n"
    car[car == False] = "1"
    car[car.isna()] = "1"

    if plot:
      pcar = car.copy()
      pcar[pcar == "n"] = 2
      pcar[pcar == "1"] = 1 
      plt = sns.heatmap(pcar.astype(float), cbar=False)
      return (car, plt)
    return (car, )