# Python | Ways to flatten a 2D list

Given a 2D list, write a Python program to convert the given list into a flattened list.

Method #1: Using` chain.iterable()`

 `# Python code to demonstrate  ` `# converting 2d list into 1d list ` `# using chain.from_iterables ` ` `  `# import chain ` `from` `itertools ``import` `chain ` ` `  `ini_list ``=` `[[``1``, ``2``, ``3``], ` `            ``[``3``, ``6``, ``7``], ` `            ``[``7``, ``5``, ``4``]] ` `             `  `# printing initial list ` `print` `(``"initial list "``, ``str``(ini_list)) ` ` `  `# converting 2d list into 1d ` `# using chain.from_iterables ` `flatten_list ``=` `list``(chain.from_iterable(ini_list)) ` ` `  `# printing flatten_list ` `print` `(``"final_result"``, ``str``(flatten_list)) `

Output:

```initial list  [[1, 2, 3], [3, 6, 7], [7, 5, 4]]
final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
```

Method #2: Using list comprehension

 `# Python code to demonstrate  ` `# converting 2d list into 1d list ` `# using list comprehension ` ` `  `# import chain ` `from` `itertools ``import` `chain ` ` `  `ini_list ``=` `[[``1``, ``2``, ``3``], ` `            ``[``3``, ``6``, ``7``], ` `            ``[``7``, ``5``, ``4``]] ` `             `  `# printing initial list ` `print` `(``"initial list "``, ``str``(ini_list)) ` ` `  `# converting 2d list into 1d ` `# using list comprehension ` `flatten_list ``=` `[j ``for` `sub ``in` `ini_list ``for` `j ``in` `sub] ` ` `  `# printing flatten_list ` `print` `(``"final_result"``, ``str``(flatten_list)) `

Output:

```initial list  [[1, 2, 3], [3, 6, 7], [7, 5, 4]]
final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
```

Method #3: Using `functools.reduce`

 `# Python code to demonstrate  ` `# converting 2d list into 1d list ` `# using functools.reduce ` ` `  `# import functools ` `from` `functools ``import` `reduce` ` `  `ini_list ``=` `[[``1``, ``2``, ``3``], ` `            ``[``3``, ``6``, ``7``], ` `            ``[``7``, ``5``, ``4``]] ` `             `  `# printing initial list ` `print` `(``"initial list "``, ``str``(ini_list)) ` ` `  `# converting 2d list into 1d ` `# using functools.reduce ` `flatten_list ``=` `reduce``(``lambda` `z, y :z ``+` `y, ini_list) ` ` `  `# printing flatten_list ` `print` `(``"final_result"``, ``str``(flatten_list)) `

Output:

```initial list  [[1, 2, 3], [3, 6, 7], [7, 5, 4]]
final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
```

Method #4: Using `sum`
sum has an optional argument: sum(iterable [, start])

 `# Python code to demonstrate  ` `# converting 2d list into 1d list ` `# using sum ` ` `  `ini_list ``=` `[[``1``, ``2``, ``3``], ` `            ``[``3``, ``6``, ``7``], ` `            ``[``7``, ``5``, ``4``]] ` ` `  `# printing initial list  ` `print` `(``"initial list "``, ``str``(ini_list)) ` ` `  `# converting 2d list into 1d ` `flatten_list ``=` `sum``(ini_list, []) ` ` `  `# printing flatten_list  ` `print` `(``"final_result"``, ``str``(flatten_list)) ` ` `  `# This code is contributed by ` `# Mayank Chaudhary - chaudhary_19 `

Output:

```initial list  [[1, 2, 3], [3, 6, 7], [7, 5, 4]]
final_result [1, 2, 3, 3, 6, 7, 7, 5, 4]
```

Method #5: Using `lambda`

 `#Python 3 code to flatten nested list ` `#contributed by S Lakshman Rao - kaapalx ` `ini_list``=``[[``1``, ``2``, ``3``], ` `          ``[``3``, ``6``, ``7``], ` `          ``[``7``, ``5``, ``4``]] ` ` `  `#Using lambda ` ` `  `flatten_list ``=` `lambda` `y:[x ``for` `a ``in` `y ``for` `x ``in` `flatten_list(a)] ``if` `type``(y) ``is` `list` `else` `[y] ` ` `  `print``(``"Initial list "``,ini_list) ``#priniting initial list ` ` `  `print``(``"Flattened List "``,flatten_list(ini_list)) ``# printing flattened list `

Output:

```Initial list  [[1, 2, 3], [3, 6, 7], [7, 5, 4]]
Flattened List  [1, 2, 3, 3, 6, 7, 7, 5, 4]
```

Method #6: Using `numpy`

 `#Python 3 code to flatten nested list ` `#Contributed by S Lakshman Rao - kaapalx ` `import` `numpy ` ` `  `ini_list``=``[[``1``, ``2``, ``3``], ` `          ``[``3``, ``6``, ``7``], ` `          ``[``7` `,``5``, ``4``]] ` ` `  `print``(``"Initial list "``,ini_list) ``#Printing Initial list ` ` `  `print``(``"Flattened List "``,``list``(numpy.concatenate(ini_list).flat)) ` `#Using numpy to flatten list and printing the result `

Output:

```Initial list  [[1, 2, 3], [3, 6, 7], [7, 5, 4]]
Flattened List  [1, 2, 3, 3, 6, 7, 7, 5, 4]
```

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Improved By : chaudhary_19, kaapalx