Question

I am looping through lines of a csv in order to extract and transform data.

the csv looks like this:

alex, blue, 3
alex, blue, 4
liza, green, 2
alex, red, 4
alex, orange, 3
liza, blue, 2
liza, blue, 21
liza, yellow, 23

the result i want from the above are 2 files:

alex file

<blue>3, 4</blue>
<red>4</red>
<orange>3</orange>

liza file

<green>2</green>
<blue>2,21</blue>
<yellow>23</yellow>

i am not looking for you to solve this problem for me, but i am just looking for your guidance. i dont need help with the xml part, i would just like help on the LOGIC part.

thanks so much!

Answer 1

My preferred datastructure here (assuming order of names and colours isn’t important!) would be a nested defaultdict. The usual usage is something like this:

>>> from collections import defaultdict
>>> d = defaultdict(list)
>>> d['blue'].append(3)
>>> d['blue'].append(4)
>>> d
defaultdict(<type 'list'>, {'blue': [3, 4]})

But we can also go one level deeper:

>>> d = defaultdict(lambda: defaultdict(list))
>>> d
defaultdict(<function <lambda> at 0x1004bf9b0>, {})
>>> d['alex']['blue'].append(3)
>>> d['alex']['blue'].append(4)
>>> d['liza']['green'].append(2)
>>> d
defaultdict(<function <lambda> at 0x1004bf9b0>, {'liza': defaultdict(<type 'list'>, {'green': [2]}), 'alex': defaultdict(<type 'list'>, {'blue': [3, 4]})})
>>> d.keys()
['liza', 'alex']
>>> d['alex'].keys()
['blue']
>>> d['alex']['blue']
[3, 4]