Python retrieve values in list from set of tuples

Question

Suppose I have a ordered list here called T

T = ['foo', 'bar', 'cad']

I then have a set M containing tuples.

M = { 
        ('jack', 'bar'), 
        ('bob', 'foo'), 
        ('let', 'cad') 
    }

For every item in T, I want to find the corresponding tuple pair in M. So my output would look like the following list

O = [ 'bob', 'jack', 'let' ]

I tried this set comprehension but this of course just iterated the elements as defined in the order of M, I need to define it in the order of T.

answer = [ a for (a,b) in R if b in T ]

As a follow up question, say my M looked like:

M = { 
        ('bar', 'jack'), 
        ('foo', 'bob'), 
        ('cad', 'let') 
    }

Does this make this easier to solve?

Is it possible to solve this without using a dict? Purely lists, sets and tuples?

Your expected output is not possible, in the sense that you expect a set in a specific order, but sets are unordered. — deceze
– deceze ♦, Commented May 28, 2021 at 12:31
Sorry, typo on my part I want my expected answer to be a List. — DanielJ
– DanielJ, Commented May 28, 2021 at 12:35
@DanielJ if an answer here solves your problem, please accept it — Be Chiller Too
– Be Chiller Too, Commented May 28, 2021 at 15:48

Be Chiller Too · Accepted Answer · 2021-05-28 12:31:54Z

1

T = ['foo', 'bar', 'cad']

M = { 
        ('jack', 'bar'), 
        ('bob', 'foo'), 
        ('let', 'cad') 
    }

d = {k:v for (v,k) in M}

answer = [d[elt] for elt in T]

print(answer)
# ['bob', 'jack', 'let']

answered May 28, 2021 at 12:31

Be Chiller Too

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Comments

Ayus Mohanty · Accepted Answer · 2021-05-28 12:45:29Z

0

T = ['foo', 'bar', 'cad']
M = { 
        ('jack', 'bar'), 
        ('bob', 'foo'), 
        ('let', 'cad') 
    }

# Solution 1 - Order is different everytime
a = [x for (x, y) in M if y in T]
print(a)

# Solution 2 - Give you answer in same order always
MT = {y:x for (x, y) in M}
a = [MT[i] for i in T]
print(a)

You can try this.

answered May 28, 2021 at 12:45

Ayus Mohanty

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