Convert a list of tuples to a dictionary

Question

I have a list of tuples with three elements:

A = [[(72, 1, 2), (96, 1, 4)], 
     [(72, 2, 1), (80, 2, 4)], 
     [], 
     [(96, 4, 1), (80, 4, 2), (70, 4, 5)],
     [(70, 5, 4)],
     ]

I need to convert it to a dictionary in this format (note that the second element in the tuple will be the key):

A_dict = { 1: {2:72, 4:96},
           2: {1:72, 4:80},
           3: {},
           4: {1:96, 2:80, 5:70},
           5: {4:70},
         }

Is there a way to convert A to A_dict?

I tried this:

A_dict = {b:{a:c} for a,b,c in A}

but I got an error:

ValueError: not enough values to unpack (expected 3, got 2)

Yes, there is a way. Please show your attempts from your research and explain what went wrong. — roganjosh, Dec 04 '18 at 20:42
Possible duplicate : https://stackoverflow.com/questions/6522446/list-of-tuples-to-dictionary — GodSaveTheDucks, Dec 04 '18 at 20:46
Possible duplicate of [List of tuples to dictionary](https://stackoverflow.com/questions/6522446/list-of-tuples-to-dictionary) — Dexygen, Dec 04 '18 at 20:47

score 3 · Accepted Answer · answered Dec 04 '18 at 20:46

3

You can just do:

A_dict = {k+1: {t[2]: t[0] for t in l} for k, l in enumerate(A)}

>>> A_dict
{
 1: {2: 72, 4: 96}, 
 2: {1: 72, 4: 80}, 
 3: {}, 
 4: {1: 96, 2: 80, 5: 70}, 
 5: {4: 70}
}

answered Dec 04 '18 at 20:46

bphi

3,115
3
23
36

While this works on the OP's stated input, I'm not sure we can take for granted that the second element of each tuple is always one greater than its index in A. In other words, `k+1` seems like a brittle solution for determining the key of `A_dict`. – Kevin Dec 04 '18 at 20:56
@Kevin Doesn't `k` come from `enumerate` though? – Cole Dec 04 '18 at 21:08

Dinari · Answer 2 · 2018-12-04T21:03:15.840

2

By iterating on the indices of the list, according to its length. And for each value building its own dictionary:

A_dict = {i + 1 : {v[2] : v[0] for v in A[i]} for i in range(len(A))}

will output:

{1: {2: 72, 4: 96},
 2: {1: 72, 4: 80},
 3: {},
 4: {1: 96, 2: 80, 5: 70},
 5: {4: 70}}

Actually your desired code is:

A_dict = {A[i][0][1] : {v[2] : v[0] for v in A[i]} for i in range(len(A)) if len(A[i]) > 0}

But that will 'skip' the third line, as there is no list, thus not able to determinate the actual key, according to your specification.

edited Dec 04 '18 at 21:03

answered Dec 04 '18 at 20:46

Dinari

2,487
13
28

While this works on the OP's stated input, I'm not sure we can take for granted that the second element of each tuple is always one greater than its index in A. In other words, `i+1` seems like a brittle solution for determining the key of `A_dict`. – Kevin Dec 04 '18 at 20:56
You are correct, but that is not consistent with his expected output, I will, however, fix this. – Dinari Dec 04 '18 at 21:00

Convert a list of tuples to a dictionary

2 Answers2