Having an csv file with 3 columns I an trying to make a dictionary. First I read the file:
fin = open('example.csv', 'r')
with these columns how I could make a dictionary?
4 Answers
EDITED in response to OP comment
I think what you are asking for is to turn
a,123,456
b,333,444
c,888,3434
into
{'a': ('123', '456'), 'b': ('333', '444'), 'c': ('888', '3434')}
If so, one solution is to use csv.reader to parse the file, iterate the rows and populate your final dict.
with open('example.txt', 'rb') as src_file:
csv_file = csv.reader(src_file)
data = {}
for row in csv_file:
data[row[0]] = (row[1], row[2])
print(data)
See the csv module docs at http://docs.python.org/2/library/csv.html
3 Comments
Rob Cowie
If your data file is huge and memory is an issue, there are more efficient ways to do this using generators. Please comment if this is the case.
Rob Cowie
Actually, I didn't give that comment enough thought; If you want to turn the entire file into a dict (in memory) then reading it all is unavoidable. If you have duplicate keys (in column 1) then naturally some of the file will be 'ignored'. Else, it will be difficult to improve memory efficiency. How huge are your files?
Rob Cowie
It seems that reading it all into memory is unavoidable. It depends what you are trying to do with the data. Is there any way you can work with it in chunks? What is the data? What are you doing with it? It may not be a problem. Work with it and see how it performs.
you can use dict_writer in csv module.
import csv
fieldnames = ['Column1', 'Column2', 'Column3']
dict_writer = csv.DictWriter(file('your.csv', 'wb'), fieldnames=fieldnames)
dict_writer.writerow(fieldnames)
dict_writer.writerows(rows)
1 Comment
Jon Clements
I think the OP is after creating a
dict from a CSV fileYou didn't say how the values should look like, so:
d={}
with open('example.csv', 'r') as file:
for line in file:
lst = line.strip().split(',')
d[lst[0]] = lst[1:]
This outputs something like:
{'key1': ['v1', 'v2'], 'key2': ['v1', 'v2']}
4 Comments
iabdalkader
@HelenFirstrofen what do you mean ?
iabdalkader
@HelenFirstrofen
lst[0] is the first column in the csv file and lst[1:] is the remaining columns, and yes you can read all the lines once from file using file.readlines()
Helen Firstrofen
I am asking this because it gives me back this error ValueError: I/O operation on closed file
iabdalkader
@HelenFirstrofen ah I see, after the
with open(...) block the file is closed automatically, if you still want to access the file after that then you should use f=open(...) instead.You can also use numpy loadtxt and create the dict.
from numpy import loadtxt
a,b,c = loadtxt('filename.csv', sep=',', unpack=true)
dictionary = dict(zip(a,(b,c)))
csvmodule instead.