How to convert list of tuples as dictionary of lists with common item from tuple as key of dictionar-CodePudding

Suppose i have list of lists

list_l = [ ['txt1', 'val1'], ['txt2', 'val2'], ['txt1', 'val3'], ['txt1', 'val5'] ]

I want to transform this as dictionary below

dict_result = {'txt1': ['val1', 'val3', 'val5'], 'txt2': ['val2']}

Also there are performance requirements as the original list is from ~800mb of file contents.

CodePudding user response：

It's a simple for-loop :

dictionnary = {}
for i in list_l:
    if i[0] not in dictionnary:
        dictionnary[i[0]] = []
        dictionnary[i[0]].append(i[1])
    else:
        dictionnary[i[0]].append(i[1])

But yeah, for a list of 800mb you should take a look to those librairies like @9769953 told you

CodePudding user response：

as @AxelRozental suggests but utilizing the dictionary pop feature:

dictionary = {}

for i in list:
    k = dictionary.pop(i[0], [])
    k.append(i[1])
    dictionary[i[0]] = k

CodePudding user response：

The defaultdict data structure is the simplest way.

You can do a single scan in the list and collect incrementally the second element

from collections import defaultdict
list_l = [ ['txt1', 'val1'], ['txt2', 'val2'], ['txt1', 'val3'], ['txt1', 'val5'] ]
out = defaultdict(list)
for k, v in list_l:
    out[k].append(v)

# defaultdict(list, {'txt1': ['val1', 'val3', 'val5'], 'txt2': ['val2']})

If the data amount could be critical consider to 'consume' the original list using pop function (as already told)