Save results to csv file with Python

import csv

with open('test.csv', 'rb') as f:
  data = list(csv.reader(f))

import collections
counter = collections.defaultdict(int)
for row in data:
    counter[row[1]] += 1
for row in data:
    if counter[row[1]] >= 4:
      writer = csv.writer(open("test1.csv", "wb"))
      writer.writerows(row)

I am getting strange output! What is wrong with this code?

I know the question is asking about your "csv" package implementation, but for your information, there are options that are much simpler — numpy, for instance.

import numpy as np
np.savetxt('data.csv', (col1_array, col2_array, col3_array), delimiter=',')

(This answer posted 6 years later, for posterity's sake.)

In a different case similar to what you're asking about, say you have two columns like this:

names = ['Player Name', 'Foo', 'Bar']
scores = ['Score', 250, 500]

You could save it like this:

np.savetxt('scores.csv', [p for p in zip(names, scores)], delimiter=',', fmt='%s')

scores.csv would look like this:

Player Name,Score
Foo,250
Bar,500

Use csv.writer:

import csv

with open('thefile.csv', 'rb') as f:
  data = list(csv.reader(f))

import collections
counter = collections.defaultdict(int)
for row in data:
    counter[row[0]] += 1


writer = csv.writer(open("/path/to/my/csv/file", 'w'))
for row in data:
    if counter[row[0]] >= 4:
        writer.writerow(row)

You can close files not csv.writer object, it should be:

f = open(fileName, "wb")
writer = csv.writer(f)
String[] entries = "first*second*third".split("*");
writer.writerows(entries)
f.close()

You can save it as follow if you have Pandas Dataframe

   df.to_csv(r'/dir/filename.csv')

An easy example would be something like:

writer = csv.writer(open("filename.csv", "wb"))
String[] entries = "first#second#third".split("#");
writer.writerows(entries)
writer.close()