python - Write dictionary of lists to a CSV file

Question

I'm struggling with writing a dictionary of lists to a .csv file.

This is how my dictionary looks like:

dict[key1]=[1,2,3]
dict[key2]=[4,5,6]
dict[key3]=[7,8,9]

I want the .csv file to look like:

key1  key2  key3
1     4     7  
2     5     8
3     6     9

At first I write the header:

outputfile = open (file.csv,'wb')
writefile = csv.writer (outputfile)
writefile.writerow(dict.keys())

So far so good... However, my problem is that I don't know how I could assign one list to the corresponding column. e.g.:

for i in range(0,len(dict[key1])):
    writefile.writerow([dict[key1][i],dict[key2][i],dict[key3][i])

will randomly fill the columns. Another problem is, that I have to manually fill in the keys and can't use it for another dictionary with 4 keys.

Answer 1

If you don't care about the order of your columns (since dictionaries are unordered), you can simply use zip():

d = {"key1": [1,2,3], "key2": [4,5,6], "key3": [7,8,9]}
with open("test.csv", "wb") as outfile:
   writer = csv.writer(outfile)
   writer.writerow(d.keys())
   writer.writerows(zip(*d.values()))

Result:

key3    key2    key1
7       4       1
8       5       2
9       6       3

If you do care about order, you need to sort the keys:

keys = sorted(d.keys())
with open("test.csv", "wb") as outfile:
   writer = csv.writer(outfile, delimiter = "")
   writer.writerow(keys)
   writer.writerows(zip(*[d[key] for key in keys]))

Result:

key1    key2    key3
1       4       7
2       5       8
3       6       9