gaspersic/freeCodeCamp
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Fix(guide): Reformat article

Browse Source
This commit is contained in:
theodoreyoong
2018-10-21 19:26:29 +01:00
committed by Heather Kusmierz
parent 9309f0f6c0
commit 5e8d071a18
1 changed files with 30 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

48
guide/english/python/itertools/index.md
View File

@ -5,10 +5,11 @@ title: Itertools
Itertools is a python module of functions that return generators, objects that only function when iterated over. Itertools is a python module of functions that return generators, objects that only function when iterated over.
Some examples of itertool functions include but not limited to: chain(), imap(), product(), and compress(). Some examples of itertool functions include but not limited to: chain(), imap(), product(), and compress().
### Iterators terminating on the shortest input sequence:
### chain() #### chain()
The chain() function takes several iterators as arguments and returns a single iterator that produces the contents of all of them as though they came from one sequence. The `chain()` function takes several iterators as arguments and returns a single iterator that produces the contents of all of them as though they came from one sequence.
```py ```py
import itertools import itertools
@ -18,10 +19,9 @@ list(itertools.chain([1, 2], [3, 4]))
# [1, 2, 3, 4] # [1, 2, 3, 4]
``` ```
#### islice()
### islice() The `islice()` function returns an iterator which returns selected items from the input iterator, by index. It takes the same arguments as the slice operator for lists: start, stop, and step. Start and stop are optional.
The islice() function returns an iterator which returns selected items from the input iterator, by index. It takes the same arguments as the slice operator for lists: start, stop, and step. Start and stop are optional.
```py ```py
import itertools import itertools
@ -31,9 +31,9 @@ list(itertools.islice(count(), 5))
# [0,1, 2, 3, 4] # [0,1, 2, 3, 4]
``` ```
### izip() #### izip()
izip() returns an iterator that combines the elements of several iterators into tuples. It works like the built-in function zip(), except that it returns an iterator instead of a list. `izip()` returns an iterator that combines the elements of several iterators into tuples. It works like the built-in function `zip()`, except that it returns an iterator instead of a list.
```py ```py
import itertools import itertools
@ -43,19 +43,31 @@ list(izip([1, 2, 3], ['a', 'b', 'c']))
# [(1, 'a'),(2, 'b'),(3, 'c')] # [(1, 'a'),(2, 'b'),(3, 'c')]
``` ```
Combinatoric iterators: ### Combinatoric iterators
Iterator Arguments Results #### product()
product() p, q, … [repeat=1] cartesian product, equivalent to a nested for-loop
permutations() p[, r] r-length tuples, all possible orderings, no repeated elements
combinations() p, r r-length tuples, in sorted order, no repeated elements
combinations_with_replacement() p, r r-length tuples, in sorted order, with repeated elements
product('ABCD', repeat=2) AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD
permutations('ABCD', 2) AB AC AD BA BC BD CA CB CD DA DB DC
combinations('ABCD', 2) AB AC AD BC BD CD `product()` returns a Cartesian product, equivalent to a nested for-loop. In comparison, the usual `zip()` function, which returns the convolution.
combinations_with_replacement('ABCD', 2) AA AB AC AD BB BC BD CC CD DD ```py
from itertools import product
list(product([1,2,3],[3,4]))
# Output
# [(1, 3), (1, 4), (2, 3), (2, 4), (3, 3), (3, 4)]
Source:https://docs.python.org/3/library/itertools.html A = [[1,2,3],[3,4,5]]
list(product(*A))
# Output
# [(1, 3), (1, 4), (1, 5), (2, 3), (2, 4), (2, 5), (3, 3), (3, 4), (3, 5)]
B = [[1,2,3],[3,4,5],[7,8]]
list(product(*B))
# Output
# [(1, 3, 7), (1, 3, 8), (1, 4, 7), (1, 4, 8), (1, 5, 7), (1, 5, 8), (2, 3, 7), (2, 3, 8), (2, 4, 7), (2, 4, 8), (2, 5, 7), (2, 5, 8), (3, 3, 7), (3, 3, 8), (3, 4, 7), (3, 4, 8), (3, 5, 7), (3, 5, 8)]
```
Source: https://docs.python.org/3/library/itertools.html
https://www.hackerrank.com/challenges/itertools-product/problem