Python Joining csv files where key is first column value

Question

I try to join two csv files where key is value of first column. There's no header. Files have different number of lines and rows. Order of file a must be preserved. file a: ``` john,red,34 andrew,green,18 tonny,black,50 jack,yellow,27 phill,orange,45 kurt,blue,29 mike,pink,61 ``` file b: ``` tonny,driver,new york phill,scientist,boston ``` desired result: ``` john,red,34 andrew,green,18 tonny,black,50,driver,new york jack,yellow,27 phill,orange,45,scientist,boston kurt,blue,29 mike,pink,61 ``` I examined all related threads and I am sure that some of you are gonna mark this question duplicate but I simply have not found solution yet. I grabbed dictionary based solution but this approach does not handle preserve line order from file 'a' condition. ``` import csv from collections import defaultdict with open('a.csv') as f: r = csv.reader(f, delimiter=',') dict1 = {} for row in r: dict1.update({row[0]: row[1:]}) with open('b.csv') as f: r = csv.reader(f, delimiter=',') dict2 = {} for row…

Accepted Answer

Something like

```
import csv
from collections import OrderedDict

with open('b.csv', 'rb') as f:
    r = csv.reader(f)
    dict2 = {row[0]: row[1:] for row in r}

with open('a.csv', 'rb') as f:
    r = csv.reader(f)
    dict1 = OrderedDict((row[0], row[1:]) for row in r)

result = OrderedDict()
for d in (dict1, dict2):
    for key, value in d.iteritems():
        result.setdefault(key, []).extend(value)

with open('ab_combined.csv', 'wb') as f:
    w = csv.writer(f)
    for key, value in result.iteritems():
        w.writerow([key] + value)
```

produces

```
john,red,34
andrew,green,18
tonny,black,50,driver,new york
jack,yellow,27
phill,orange,45,scientist,boston
kurt,blue,29
mike,pink,61
```

(Note that I didn't bother protecting against the case where `dict2` has a key which isn't in `dict1`-- that's easily added if you like.)

Python Joining csv files where key is first column value

Solution

Problem