I have a list of words that I am trying to sort within a list:

words = ["yo", "act", "flop",'tac']

words = list(map(sorted,words))


Desired outcome: ['oy','act','flop','act']

The above splits up each word inside words into individual characters- but does sort it:

1. why does it do this? Because we are just sorting?
2. how can I rejoin them so that they are words again rather than individual characters? I know it is using "".join(), but I can't seem to wrap this around the above!

Thanks!

CodePudding user response：

sorted works on arbitrary iterable values, but always returns a list, not a value of the same iterable it just sorted.

>>> sorted("yo")
['o', 'y']

That means you have to take the sorted list and turn it back into a string yourself.

>>> [''.join(sorted(x)) for x in words]
['oy', 'act', 'flop', 'act']

You can still use map, but it's a little messier than just using a list comprehension:

>>> list(map(lambda x: ''.join(sorted(x)), words))
['oy', 'act', 'flop', 'act']

Because Python doesn't support function composition natively, you can't write something concise (and possibly more efficient) like

list(map(''.join ∘ sorted, words))

(where ∘ is a hypothetical operator that behaves like

(f ∘ g) == lambda x: f(g(x))

)

Composition always involves creating an additional function that needs to be called in order to call the original two functions, rather than creating a separate single function that does the same thing as the original two.

The other alternative (list(map(''.join, map(sorted, words)))) isn't much better; although map(f∘g, x) is generally equivalent in effect to map(f, map(g, x)), now you are iterating over the sequence twice (or rather, iterating over one sequence, then iterating over a second intermediate sequence).

CodePudding user response：

If it doesn't already have a name, you need to define the function that you want to map over the list.

You can define a function either with def, or with lambda.

words = ["yo", "act", "flop",'tac']

def f(w):
  return ''.join(sorted(w))

print( list(map(f, words)) )
# ['oy', 'act', 'flop', 'act']

print( list(map(lambda w: ''.join(sorted(w)), words)) )
# ['oy', 'act', 'flop', 'act']

CodePudding user response：

You can also use join in the map function call:

words = list(map(lambda x: "".join(sorted(x)),words))
print(words)
>>> ['oy', 'act', 'flop', 'act']