Kevin - 1 year ago 34

Python Question

There's a bunch of questions that are phrased similarly, but I was unable to find one that actually mapped to my intended semantics.

There are two lists,

`A`

`B`

`B`

`A`

`B`

`A`

Note that

`A`

As an example, if the following were input:

`a = [7, 14, 0, 9, 19, 9]`

b = [45, 42, 0, 1, -1, 0]

I want the output to be

`[0, 42, -1, 0, 45, 1]`

Please note that the intended output is not

`[0, 45, 1, 0, 42, -1]`

`A`

`B`

Here's my code:

`def get_swaps(x):`

out = []

if len(x) <= 1:

return out

y = x[:]

n = -1

while len(y) != 1:

pos = y.index(max(y))

y[pos] = y[-1]

y.pop()

out.append((pos, n))

n -= 1

return out

def apply_swaps_in_reverse(x, swaps):

out = x[:]

for swap in swaps[::-1]:

orig, new = swap

out[orig], out[new] = out[new], out[orig]

return out

def reorder(a, b):

return apply_swaps_in_reverse(sorted(b), get_swaps(a))

The approach is basically to construct a list of the swaps necessary to sort

`A`

`B`

Answer Source

```
a = [7, 14, 0, 9, 19, 9]
b = [45, 42, 0, 1, -1, 0]
print zip(*sorted(zip(sorted(b), sorted(enumerate(a), key=lambda x:x[1])), key=lambda x: x[1][0]))[0]
#or, for 3.x:
print(list(zip(*sorted(zip(sorted(b), sorted(enumerate(a), key=lambda x:x[1])), key=lambda x: x[1][0])))[0])
```

result:

```
(0, 42, -1, 0, 45, 1)
```

You sort `a`

, using `enumerate`

to keep track of each item's original index. You zip the result with `sorted(b)`

, then re-sort the whole thing based on `a`

's original indices. Then you call `zip`

once more to extract just `b`

's values.