**Shortest Code**

```
[x for _, x in sorted(zip(Y, X))]
```

**Example:**

```
X = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]
Y = [ 0, 1, 1, 0, 1, 2, 2, 0, 1]
Z = [x for _,x in sorted(zip(Y,X))]
print(Z) # ["a", "d", "h", "b", "c", "e", "i", "f", "g"]
```

**Generally Speaking**

```
[x for _, x in sorted(zip(Y, X), key=lambda pair: pair[0])]
```

**Explained:**

`zip`

the two`list`

s.- create a new, sorted
`list`

based on the`zip`

using`sorted()`

. - using a list comprehension
*extract*the first elements of each pair from the sorted, zipped`list`

.

*For more information on how to set\use the key parameter as well as the sorted function in general, take a look at this.*