Modified Z Score

# coding: utf-8

import os
import sys
import math
from statistics import median
import numpy as np
import pandas as pd

in_file = 'data.csv'


df = pd.read_csv(in_file)
# Round position to tenths
df = df.round({'position': 1})


def apply_stats(row, df):
    ctr = float(row['ctr'])
    pos = float(row['position'])

    # Median
    median_ctr = median(df.ctr[df.position==pos])
    # Mad
    mad_ctr = df.ctr[df.position==pos].mad()

    row['score'] = round(float( (0.6745 * (ctr - median_ctr))/mad_ctr ), 3 )
    row['mad'] = mad_ctr
    row['median'] = median_ctr

    return row


# Modified z-score = (constant of 0.6745 * (individual CTR – median CTR of a given position)) / median absolute deviation for a CTR at a given position


df = df.apply(apply_stats, args=(df,), axis = 1)


df.to_csv('out' + in_file)