Dictionary comprehension with a nested list

Question

I have a string of characters and a list of characters. I wish to create a dictionary in which the keys are the characters as and the values are the list, only without the key character.

A string of characters:

sequence = 'ATGCG'

The list:

bases = ['C', 'T', 'A', 'G']

The resulting dictionary would be:

{'A': ['C', 'T', 'G'], 'T': ['C', 'A', 'G'], 'G': ['C', 'T', 'A'], 'C': ['T', 'A', 'G'], 'G': ['C', 'T', 'A'], }

I tried using the following code but got a list of 4 items:

variations = {current_base: [base for base in bases if current_base != base] for current_base in sequence}

I'd love to get ideas regarding what I'm doing wrong. Thanks.

Does this answer your question? All combinations of a list of lists — wovano
– wovano, Commented Nov 9, 2021 at 12:42

mozway · Accepted Answer · 2021-11-09 12:56:44Z

What you want to do is impossible, a dictionary cannot have duplicated keys.

{'A': ['C', 'T', 'G'], 'T': ['C', 'A', 'G'], 'G': ['C', 'T', 'A'], 'C': ['T', 'A', 'G'], 'G': ['C', 'T', 'A'], ## this is impossible }

You can use a list of tuples instead. I am taking the opportunity to show you a more efficient method using python sets:

sequence = 'ATGCG' bases = set(list('ACGT')) [(b,list(bases.difference(b))) for b in sequence]

NB. actually, it is even more efficient to pre-compute the diffs as you have a potentially very long DNA sequence, but only 4 bases:

sequence = 'ATGCG' bases = set(list('ACGT')) diffs = {b: list(bases.difference(b)) for b in bases} [(b,diffs[b]) for b in sequence]

output:

[('A', ['T', 'C', 'G']), ('T', ['A', 'C', 'G']), ('G', ['T', 'A', 'C']), ('C', ['T', 'A', 'G']), ('G', ['T', 'A', 'C'])]

alternative output using the position as key:

{i: list(bases.difference(b)) for i,b in enumerate(sequence)}

output:

{0: ['T', 'C', 'G'], 1: ['A', 'C', 'G'], 2: ['T', 'A', 'C'], 3: ['T', 'A', 'G'], 4: ['T', 'A', 'C']}

Thicham · Accepted Answer · 2021-11-09 12:56:05Z

0

Try this:

sequence = 'ATGCG' d = {c: list(''.join(set(list(sequence))).replace(c,'')) for c in set(list(sequence))}

edited Nov 9, 2021 at 12:56

answered Nov 9, 2021 at 12:53

Thicham

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1 Comment

mozway Over a year ago

This is invalid. Duplicate keys will be overwritten by the last value.

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