Creating a dictionary from a csv file?

user_636493 0
Viewed 639878

I am trying to create a dictionary from a csv file. The first column of the csv file contains unique keys and the second column contains values. Each row of the csv file represents a unique key, value pair within the dictionary. I tried to use the csv.DictReader and csv.DictWriter classes, but I could only figure out how to generate a new dictionary for each row. I want one dictionary. Here is the code I am trying to use:

import csv

with open('coors.csv', mode='r') as infile:
    reader = csv.reader(infile)
    with open('coors_new.csv', mode='w') as outfile:
    writer = csv.writer(outfile)
    for rows in reader:
        k = rows[0]
        v = rows[1]
        mydict = {k:v for k, v in rows}
    print(mydict)

When I run the above code I get a ValueError: too many values to unpack (expected 2). How do I create one dictionary from a csv file? Thanks.

csv list-comprehension dictionary python
17 Answers

Assuming you have a CSV of this structure:

"a","b"
1,2
3,4
5,6

And you want the output to be:

[{'a': '1', ' "b"': '2'}, {'a': '3', ' "b"': '4'}, {'a': '5', ' "b"': '6'}]

A zip function (not yet mentioned) is simple and quite helpful.

def read_csv(filename):
    with open(filename) as f:
        file_data=csv.reader(f)
        headers=next(file_data)
        return [dict(zip(headers,i)) for i in file_data]

If you prefer pandas, it can also do this quite nicely:

import pandas as pd
def read_csv(filename):
    return pd.read_csv(filename).to_dict('records')
user_120141560

For simple csv files, such as the following

id,col1,col2,col3
row1,r1c1,r1c2,r1c3
row2,r2c1,r2c2,r2c3
row3,r3c1,r3c2,r3c3
row4,r4c1,r4c2,r4c3

You can convert it to a Python dictionary using only built-ins

with open(csv_file) as f:
    csv_list = [[val.strip() for val in r.split(",")] for r in f.readlines()]

(_, *header), *data = csv_list
csv_dict = {}
for row in data:
    key, *values = row   
    csv_dict[key] = {key: value for key, value in zip(header, values)}

This should yield the following dictionary

{'row1': {'col1': 'r1c1', 'col2': 'r1c2', 'col3': 'r1c3'},
 'row2': {'col1': 'r2c1', 'col2': 'r2c2', 'col3': 'r2c3'},
 'row3': {'col1': 'r3c1', 'col2': 'r3c2', 'col3': 'r3c3'},
 'row4': {'col1': 'r4c1', 'col2': 'r4c2', 'col3': 'r4c3'}}

Note: Python dictionaries have unique keys, so if your csv file has duplicate ids you should append each row to a list.

for row in data:
    key, *values = row

    if key not in csv_dict:
            csv_dict[key] = []

    csv_dict[key].append({key: value for key, value in zip(header, values)})
user_63276580

with pandas, it is much easier, for example. assuming you have the following data as CSV and let's call it test.txt / test.csv (you know CSV is a sort of text file )

a,b,c,d
1,2,3,4
5,6,7,8

now using pandas

import pandas as pd
df = pd.read_csv("./text.txt")
df_to_doct = df.to_dict()

for each row, it would be 

df.to_dict(orient='records')

and that's it.

user_79432800

Try to use a defaultdict and DictReader.

import csv
from collections import defaultdict
my_dict = defaultdict(list)

with open('filename.csv', 'r') as csv_file:
    csv_reader = csv.DictReader(csv_file)
    for line in csv_reader:
        for key, value in line.items():
            my_dict[key].append(value)

It returns:

{'key1':[value_1, value_2, value_3], 'key2': [value_a, value_b, value_c], 'Key3':[value_x, Value_y, Value_z]}
user_102707270

Many solutions have been posted and I'd like to contribute with mine, which works for a different number of columns in the CSV file. It creates a dictionary with one key per column, and the value for each key is a list with the elements in such column.

    input_file = csv.DictReader(open(path_to_csv_file))
    csv_dict = {elem: [] for elem in input_file.fieldnames}
    for row in input_file:
        for key in csv_dict.keys():
            csv_dict[key].append(row[key])
user_105798190

here is an approach for CSV to Dict:

import pandas

data = pandas.read_csv('coors.csv')

the_dictionary_name = {row.k: row.v for (index, row) in data.iterrows()}
user_147506990

If you have:

  1. Only 1 key and 1 value as key,value in your csv
  2. Do not want to import other packages
  3. Want to create a dict in one shot

Do this:

mydict = {y[0]: y[1] for y in [x.split(",") for x in open('file.csv').read().split('\n') if x]}

What does it do?

It uses list comprehension to split lines and the last "if x" is used to ignore blank line (usually at the end) which is then unpacked into a dict using dictionary comprehension.

user_42890620
Related