Convert dict to nested list, inserting keys into each sublist

Question

I have a solution to this question, but I'm curious if there might be a better way. I have a dict like this:

dict1 = {
'key1':[['value1','value2','value3'],['value4','value5','value6']],
'key2':[['value7','value8','value9'],['value10','value11','value12']],
'key3':[['value13','value14','value15'],['value16','value17','value18']]}

I want to convert this into a nested list, and inserting the keys into the new sublist like this:

nestedlist = [
['value1','value2','key1','value3'],['value4','value5','key1','value6'],
['value7','value8','key1','value9'],['value10','value11','key2','value12'],
['value13','value14','key2','value15'],['value16','value17','key2','value18'],
['value10','value11','key3','value12'],['value13','value14','key3','value15'],
['value16','value17','key3','value18']]

I solve this the following way:

keys = [*dict1]
newlist = []
for item in keys:
    for item2 in dict1[item]:
        item2.insert(2,item)
        newlist.append(item2)

so, how can i improve this piece of code?

jpp · Accepted Answer · 2018-03-02 00:18:18Z

3

Here is one way via a list comprehension:

res = [[w[0], w[1], k, w[2]] for k, v in dict1.items() for w in v]

# [['value1', 'value2', 'key1', 'value3'],
#  ['value4', 'value5', 'key1', 'value6'],
#  ['value7', 'value8', 'key2', 'value9'],
#  ['value10', 'value11', 'key2', 'value12'],
#  ['value13', 'value14', 'key3', 'value15'],
#  ['value16', 'value17', 'key3', 'value18']]

answered Mar 2, 2018 at 0:18

jpp

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2 Comments

Louvre Over a year ago

this method was the fastest, ill give you the correct answer :)

solstice333 Over a year ago

I was trying list comprehension at first but for some reason couldn't get it even though I've done multi nested list comp before. Thanks for posting this

solstice333 · Accepted Answer · 2018-03-02 00:14:03Z

1

I would've done it pretty similarly. The only differences shown here:

result = []
for k, l in dict1.items():
   for ll in l:
      ll.insert(2, k)
      result.append(ll)

No need to do list unpacking or doing [] accessing on dict1. items() returns a list of tuples containing each key and value of the dict.

answered Mar 2, 2018 at 0:14

solstice333

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1 Comment

solstice333 Over a year ago

Maybe there's something you can do with list(), map(), and lambdas but I'm not near a machine with python on it to test it out

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