CODEWITHSUNDEEP
pythoncsvdictionary
user3225439
user3225439

Reputation: 19

create a csv file from a list with dictionary elements in python

so I have a list which has 6 dicts inside and I would like to write that to a csv file. I have tried a lot of ways to do it but i have been unsuccessful so far. when i try to write it as a list it give me an error when i try to write it as a dict it also give me an error. can anyone point me in the write direction please.

     r_vals=
     [{'distance':2.35, 'mpg': 3.215, 'power': 45.0},{'distance':214.3, 'mpg':   29.3,'power': 124.0},{'distance':2.35, 'mpg': 3.215, 'power': 45.0},...{'distance':0.35, 'mpg': 45.5, 'power': 156.0}]

or if there is easier way to get it as a dataframe I would like it to look like this

    distance   mpg       power
    2.35       3.215     45.0
    214.3      29.3      124.0
    .
    . 
    0.35       45.5      156

thank you!

Upvotes: 0

Views: 170

Answers (5)

abarnert
abarnert

Reputation: 366103

"create a csv file from a list with dictionary elements in python" is exactly what csv.DictWriter does:

with open('output.csv', 'w') as f:
    csv.DictWriter(f, fieldnames=rvals[0].keys()).writerows(rvals)

(If your ultimate goal is to get some kind of data frame object, and you're just creating a CSV file because you think it's the best way to do that… then you don't have to; see Ryan G's answer for how easy pandas makes this.)

After this:

$ cat output.csv
3.215,45.0,2.35
29.3,124.0,214.3
3.215,45.0,2.35
45.5,156.0,0.35

Of course you probably want it to include the headers and/or put the columns in some particular order rather than whatever order the dict happens to have. (You don't need to do both, but if you don't do either one or the other, the CSV isn't very useful, because you'll have no idea which column means what…) Here's both:

with open('output.csv', 'w') as f:
    w = csv.DictWriter(f, fieldnames='distance mpg power'.split())
    w.writeheader()
    w.writerows(rvals)

Output:

distance,mpg,power
2.35,3.215,45.0
214.3,29.3,124.0
2.35,3.215,45.0
0.35,45.5,156.0

If you want a variation on the default CSV dialect, see Dialects and Formatting Parameters. To get exactly your desired output, just add , delimiter='\t' to the DictWriter constructor.

Upvotes: 3

Ryan G
Ryan G

Reputation: 9570

Have you looked into Pandas? http://pandas.pydata.org/

In pandas you can do this:

>>> r_vals
[{'distance': 2.35, 'power': 45.0, 'mpg': 3.215}, {'distance': 214.3, 'power': 124.0, 'mpg': 29.3}, {'distance': 2.35, 'power': 45.0, 'mpg': 3.215}, {'distance': 0.35, 'power': 156.0,'mpg': 45.5}]
>>> df = pandas.DataFrame(r_vals)
>>> df
   distance     mpg  power
0      2.35   3.215     45
1    214.30  29.300    124
2      2.35   3.215     45
3      0.35  45.500    156

and then you can do a:

df.to_csv("path.csv",index=False)

and you have saved your dictionary in both a dataframe in memory and a csv.

If you want to use just native python, then you can do something like this:

import csv
outfile = open("path.csv","w")
csv_writer = csv.write(outfile)
csv_writer.writerow(header)
header = r_vals[0].keys()
for row in r_vals:
  csv_writer.writerow(str([row[col_name]) for col_name in header])
outfile.close()

Upvotes: 5

dnfehren
dnfehren

Reputation: 821

http://docs.python.org/2/library/csv.html#csv.DictWriter should do that, it will also write a header row based on the column order you provide.

with open('/home/dnfehren/windesk/test.csv','wb') as fl:
    fc = csv.DictWriter(fl, ['distance','mpg','power'])

    for rvalnum, rval in enumerate(rvals):
        if rvalnum == 0:
            fc.writeheader()
            fc.writerow(rval)
        else:
            fc.writerow(rval)

Upvotes: 0

jonrsharpe
jonrsharpe

Reputation: 122154

You can use string formatting to do what you want:

with open(target, 'w') as f:
    f.write("distance\tmpg\tpower\n") # header
    for d in r_vals:
        f.write"{0[distance]:.2f}\t{0[mpg]:.3f}\t{0[power]:.1f}\n".format(d))

Here the format specification is 0 for the first argument to format, [key] to select the appropriate value, then .nf to give n decimal places.

Upvotes: 0

chk
chk

Reputation: 308

use tabulate

r_vals=[[2.35,3.215,45.0],[214.3,29.3,124.0],[2.35, 3.215,45.0],[0.35,45.5,156.0]]

 print tabulate.tabulate(r_vals, headers=["distance","mpg", "power"])

  distance     mpg    power
----------  ------  -------
      2.35   3.215       45
    214.3   29.3        124
      2.35   3.215       45
      0.35  45.5        156

Upvotes: 0

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