Adrien A. Adrien A. - 1 year ago 157
Python Question

Matching 2 large csv files by Fuzzy string matching in Python

I am trying to approximately match 600,000 individuals names (Full name) to another database that has over 87 millions observations (Full name) !

My first attempt with fuzzywuzzy library was way too slow, so I decided to use the module fuzzyset which is much faster. Assuming I have a computer powerful enough to load all the dataset in memory, I am doing the following with a test file of 964 observations to be matched against 50,000 observations:

import time
from cfuzzyset import cFuzzySet as FuzzySet

df1=pd.read_csv(file1,delimiter='|') # test file with 964 observations
df2=pd.read_csv(file2,delimiter='|') # test file with 50,000 observations to be matched against

a=FuzzySet() # allocate the FuzzySet object
for row in file2['name']:
a.add(str(row)) # Fill the FuzzySet object with all names from file2

start_time = time.time() # Start recording the time

dicto={'index':[],'name':[]} # Dictionary where I store the output

for names in file1['f_ofulln']:

print("--- %s seconds ---" % (time.time() - start_time))

>>> --- 39.68284249305725 seconds ---

With a much smaller dataset (964 observations matched against 50,000 observations), the time was 39 sec.

However, this is too slow if I want to perform this method on the full dataset.

Does anyone has an idea of how to improve the run time ? I think that Cython is not a possibility since I am already importing the Cython version of fuzzyset module

Many thanks,


Answer Source

So I am going to answer my own question since I found a way that is pretty fast.

I saved both databases in HDF5 format, using the panda.HDFStore and panda.to_hdf methods. I saved into one dataframe for each first letter of the last name. Then, I created a function finding the closest match, based on the python-Levenshtein module (very fast, since it is programmed in C).

And last, I sent 26 batch jobs at once, one for each letter of the lastname. That means I only match people with same initial of lastname.

Note that I also programmed the function to find closest match with birthyear not different by more than 1 year.

EDIT: Since it was requested, I am providing below a summary of my function. The main function that merges two dataframes is too long to be posted here unfortunately.

# Needed imports:
from Levenshtein import *
import pandas as pd

# Function that get the closest match of a word in a big list:

def get_closest_match(x, list_strings,fun):
    # fun: the matching method : ratio, wrinkler, ... (cf python-Levenshtein module)
    best_match = None
    highest_ratio = 0
    for current_string in list_strings.values.tolist():
        if highest_ratio!=1:
            current_score = fun(x, current_string)
            if(current_score > highest_ratio):
                highest_ratio = current_score
                best_match = current_string
    return (best_match,highest_ratio)

# the function that matches 2 dataframes (only the idea behind, since too long to write everything
dicto={'Index':[],'score':[], ...} 
def LevRatioMerge(df1,df2,fun,colname,required=[],approx=[],eps=[]):
    # Basically loop over df1 with:
    for name in df1.itertuples():

This is the idea. Hope that it is inspiring enough for your job.

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