- Ekta Aggarwal

# Zip function and zipped objects

Zip function takes multiple iterator objects as input and returns a list of aggregated tuples as an output. It acts as a one to one mapping so that various objects can be linked together.

**Syntax:**

*zip( iterator1 , iterator2, iterator3,... )*

__Topics covered:__

__Understanding with examples__

__Understanding with examples__

Let us create 2 lists: product_category and their corresponding sales.

```
product_category = ['Biscuits','Lotions','Face creams','Cold Drinks']
sales = [5000,23400,30000,15000]
```

To link the two lists together we zip them and create a **zipped_object:**

```
zipped_object = zip(product_category,sales)
print(zipped_object)
```

To view the output the a zipped object we need to define it explicitly as a set or a tuple or a list:

`list(zipped_object)`

In the output first object from both the lists have been combined in first tuple ('Biscuits',5000), second object from both the lists are combined to form second tuple('Lotions',23400) and so on.

**Zipping more than 2 objects:**

Let us create 2 lists: product_category, their corresponding sales and returns.

```
product_category = ['Biscuits','Lotions','Face creams','Cold Drinks']
sales = [5000,23400,30000,15000]
returns = [1000,1300,2139,5839]
```

Let us zip them together

```
zipped_object = zip(product_category,sales,returns)
list(zipped_object)
```

**Iterator objects have unequal lengths**

**Let us consider a situation where we have only 3 product categories but sales and returns for 4 product categories.**

```
product_category = ['Biscuits','Lotions','Face creams']
sales = [5000,23400,30000,15000]
returns = [1000,1300,2139,5839]
```

When we try to map such iterables of unequal length then the result is a zipped object has number of tuples = minimum length of iterable objects.

```
zipped_object = zip(product_category,sales,returns)
list(zipped_object)
```

In our case since sales of 15000 and returns of 5839 can't be mapped to any product category thus hey have been dropped

**Sorting the zipped objects:**

Zipping the objects is extremely useful when we want to sort multiple objects on the basis of one single iterable.

Let us reconsider our 3 lists:

```
product_category = ['Biscuits','Lotions','Face creams','Cold Drinks']
sales = [5000,23400,30000,15000]
returns = [1000,1300,2139,5839]
```

Let us zip them together.

`zipped_object = list(zip(product_category,sales,returns))`

Using **sorted **function we can sort our zipped object.

Inside the sorted function we have defined a lambda expression x:x[0] which indicates that sorting should be done by first zipped iterable i.e. product_category

```
sorted_object = sorted(zipped_object,key = lambda x:x[0])
sorted_object
```

In the following lambda expression we have x : -x[1] indicating that sorting should be done in descending order by second zipped iterable i.e. Sales

```
sorted_object = sorted(zipped_object,key = lambda x:-x[1])
sorted_object
```

Simple x : -x[2] indicating that sorting should be done in descending order by third zipped iterable i.e. Returns

```
sorted_object = sorted(zipped_object,key = lambda x:-x[2])
sorted_object
```

**Looping over zipped objects:**

We can iterate over multipe iterables in one single for loop using zipped objects (avoiding multiple for loops)

In the following code we have created two iterator objects pc and s which iterate over various values of zipped object one by one.

```
for pc,s in zip(product_category,sales):
print('Product category: ' + str(pc))
print('Sales: ' + str(s))
```

**Unzipping objects**

Zipped objects returns a list of tuples! To unpack them or unzip them we can use **zip **function, (There is no function called unzip :P)

Unzipping can be done by:

*zip(* zipped object)*

`zipped_object`

In the following code we are unzipping our zipped object using zip( *) and storing each element of the tuple in 3 different object.

Eg. from first tuple we have saved first element in unzipped_category, second element in unzipped_sales, and third element in unzipped_returns.

Similarly from second tuple each of the 3 element is saved in unzipped_category, unzipped_sales,unzipped_returns correspondingly.

```
unzipped_category, unzipped_sales,unzipped_returns = zip(*zipped_object)
print(unzipped_category)
print(unzipped_sales)
print(unzipped_returns)
```