如何在元组列表中组合元组

Question

Combining tuples in list of tuples

test_list = [([1, 2, 3], 'gfg'), ([5, 4, 3], 'cs')]

How to get this output:

[(1, 'gfg'), (2, 'gfg'), (3, 'gfg'), (5, 'cs'), (4, 'cs'), (3, 'cs')]

Answer 1

Just to go into a bit more detail about how to do this with list comprehensions and explain what they are and how they work...

To begin with, here's a fairly long-winded way of achieving what you want:

test_list = [([1, 2, 3], 'gfg'), ([5, 4, 3], 'cs')]

result = []  # set up empty list to hold the result
for group in test_list:  # loop through each 'group' in your list
    (numbers, text) = group  # unpack into the list of numbers and the text string
    for n in numbers:  # loop through the numbers
        result.append((n, text))  # add the (number, text) tuple to the result list

print(result)
# [(1, 'gfg'), (2, 'gfg'), (3, 'gfg'), (5, 'cs'), (4, 'cs'), (3, 'cs')]

So we've achieved the result using two for loops, one nested inside the other.

But there's a really neat Python construct called a list comprehension which lets you do this kind of loop in just one line.

Using an example with just a single loop:

numbers = [1, 2, 3]

doubles = []
for n in numbers:
    doubles.append(n * 2)

print(doubles)
# [2, 4, 6]

We can re-write this as the following list comprehension:

numbers = [1, 2, 3]

doubles = [n * 2 for n in numbers]

print(doubles)
# [2, 4, 6]

A list comprehension is of the form:

result = [<expression> for item in iterable]

which is equivalent to:

result = []
for item in iterable:
    result.append(<expression>)

where <expression> is something involving item .

You can also nest list comprehensions like you can nest for loops. Going back to our original problem, we need to first change it so that we 'unpack' group into numbers and text directly when we set up the for loop:

result = []
for (numbers, text) in test_list:
    for n in numbers:
        result.append((n, text))

Now imagine dragging the for loops off to the right until we can line them all up:

result = []
for (numbers, text) in test_list:
                                   for n in numbers:
                                                      result.append((n, text))

and then put the expression (ie (n, text) ) at the left:

result = [(n, text) for (numbers, text) in test_list for n in numbers]

List comprehensions may seem strange at first (especially if you're jumping straight into a double list comprehension!), but one you've got your head around how they work, they are really neat and can be very powerful! There are also similar set comprehensions and dictionary comprehensions. Read more here: https://dbader.org/blog/list-dict-set-comprehensions-in-python

Answer 2

You can use nested list comprehensions:

test_list = [([1, 2, 3], 'gfg'), ([5, 4, 3], 'cs')]

result = [(z, y) for x, y in test_list for z in x]
#          z = numbers in the lists inside the tuples
#          x = the lists inside the tuples
#          y = the strings inside the tuples

print(result)

Output:

[(1, 'gfg'), (2, 'gfg'), (3, 'gfg'), (5, 'cs'), (4, 'cs'),(3, 'cs')]

---

result = [(z, y) for x, y in test_list for z in x] is the list comprehension version for:

result = []
for x, y in test_list:
    for z in x:
        result.append((z,y))