read csv as dict but keep duplicate keys python

November 30, 2021

Hi currently trying to read in a very easy csv file that looks like this:

i don’t need the header, but i want all rows as a k,v in a dictionary but the writer overwrites the data with the last value, how do I keep these duplicates in order to keep all rows as k,v in my dict?

>Solution :

The convenient way to do it is using a defaultdict from the collections module:

# create some test data
with open("data.txt","w") as d:
    d.write("test,test_one\ndata,plaza\ndata,plazo\ndata,plozo\ndoto,plaza")

then use

from collections import defaultdict

data = defaultdict(list)

with open("data.txt") as f:
    f.readline()  # skip header

    # process remainder
    for line in f:
        line = line.strip() # remove \n
        if line:
            # extract key + value by splitting
            key,value = line.split(',',2)
            # and add it
            data[key].append(value)

print(data)            

# print converted 
print(dict(data.items()))

Output:

defaultdict(<class 'list'>, {'data': ['plaza', 'plazo', 'plozo'],
                             'doto': ['plaza']})

# converted to normal dict
{'data': ['plaza', 'plazo', 'plozo'], 'doto': ['plaza']}

See How does collections.defaultdict work?