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Vasudev Ram: Multiple item search in an unsorted list in Python

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[开发(python) 所属分类 开发(python) | 发布者 店小二05 | 时间 2019 | 作者 红领巾 ] 0人收藏点击收藏

- By Vasudev Ram - Online python training / SQL training / linux training


Vasudev Ram: Multiple item search in an unsorted list in Python

Hi, readers,

I was reviewing simple algorithms with a view to using some as examples or exercises in my Python programming course . While doing so, I thought of enhancing simple linear search for one item in a list, to make it search for multiple items.

Here are a couple of program versions I wrote for that task. They use straightforward logic. There are just a few additional points:

- In both programs, I use a generator to yield the values found (the index and the item).

- In the first program, I print out the index and item for each item found.

- In the second program, I mark where the items are found with text "arrows".

This is the first program, mult_item_search_unsorted_list.py :

# mult_item_search_unsorted_list.py # Purpose: To search for multiple items in an unsorted list. # Prints each item found and its index. # Author: Vasudev Ram # Copyright 2019 Vasudev Ram # Training: https://jugad2.blogspot.com/p/training.html # Blog: https://jugad2.blogspot.com # Web site: https://vasudevram.github.io # Product store: https://gumroad.com/vasudevram from __future__ import print_function import sys from random import sample, shuffle def mult_item_search_unsorted_list(dlist, slist): for didx, ditem in enumerate(dlist): for sitem in slist: if sitem == ditem: yield (didx, ditem) def main(): # Create the search list (slist) with some items that will be found # and some that will not be found in the data list (dlist) below. slist = sample(range(0, 10), 3) + sample(range(10, 20), 3) # Create the data list. dlist = range(10) for i in range(3): # Mix it up, DJ. shuffle(slist) # MIX it up, DEK. shuffle(dlist) print("\nSearching for:", slist) print(" in:", dlist) for didx, ditem in mult_item_search_unsorted_list(dlist, slist): print(" found {} at index {}".format(ditem, didx)) main()

Output of a run:

$ python mult_item_search_unsorted_list.py Searching for: [1, 18, 3, 15, 19, 4] in: [8, 9, 1, 2, 0, 7, 5, 3, 6, 4] found 1 at index 2 found 3 at index 7 found 4 at index 9 Searching for: [4, 19, 18, 15, 1, 3] in: [7, 5, 8, 2, 9, 4, 0, 3, 6, 1] found 4 at index 5 found 3 at index 7 found 1 at index 9 Searching for: [1, 3, 4, 18, 19, 15] in: [9, 6, 1, 8, 7, 4, 3, 0, 2, 5] found 1 at index 2 found 4 at index 5 found 3 at index 6

And this is the second program, mult_item_search_unsorted_list_w_arrows.py :

# mult_item_search_unsorted_list_w_arrows.py # Purpose: To search for multiple items in an unsorted list. # Marks the position of the items found with arrows. # Author: Vasudev Ram # Copyright 2019 Vasudev Ram # Training: https://jugad2.blogspot.com/p/training.html # Blog: https://jugad2.blogspot.com # Web site: https://vasudevram.github.io # Product store: https://gumroad.com/vasudevram from __future__ import print_function import sys from random import sample, shuffle def mult_item_search_unsorted_list(dlist, slist): for didx, ditem in enumerate(dlist): for sitem in slist: if sitem == ditem: yield (didx, ditem) def main(): # Create the search list (slist) with some items that will be found # and some that will not be found in the data list (dlist) below. slist = sample(range(10), 4) + sample(range(10, 20), 4) # Create the data list. dlist = range(10) for i in range(3): # Mix it up, DJ. shuffle(slist) # MIX it up, DEK. shuffle(dlist) print("\nSearching for: {}".format(slist)) print(" in: {}".format(dlist)) for didx, ditem in mult_item_search_unsorted_list(dlist, slist): print("---------{}^".format('---' * didx)) main()

Output of a run:

$ python mult_item_search_unsorted_list_w_arrows.py Searching for: [16, 0, 15, 4, 6, 1, 10, 12] in: [8, 9, 0, 1, 5, 4, 7, 2, 6, 3] ---------------^ ------------------^ ------------------------^ ---------------------------------^ Searching for: [6, 16, 10, 0, 1, 4, 12, 15] in: [2, 7, 0, 8, 1, 4, 6, 3, 9, 5] ---------------^ ---------------------^ ------------------------^ ---------------------------^ Searching for: [0, 12, 4, 10, 6, 16, 1, 15] in: [8, 1, 0, 7, 9, 6, 2, 5, 4, 3] ------------^ ---------------^ ------------------------^ ---------------------------------^

In a recent post, Dynamic function creation at run time with Python's eval built-in , I had said:

"Did you notice any pattern to the values of g(i)? The values are 1, 4, 9, 16, 25 - which are the squares of the integers 1 to 5. But the formula I entered for g was not x * x, rather, it was x * x + 2 * x + 1. Then why are squares shown in the output? Reply in the comments if you get it, otherwise I will answer next time."

No reader commented with a solution. So here is a hint to figure it out:

What is the expansion of (a + b) ** 2 (a plus b the whole squared) in algebra?

Heh.

The drawing of the magnifying glass at the top of the post is by:

Yours truly.

( The same one that I used in this post:

Command line D utility - find files matching a pattern under a directory )

I'll leave you with another question: What, if any, could be the advantage of using Python generators in programs like these?

Notice that I said " programs like these ", not " these programs ".

Enjoy.

- Vasudev Ram - Online Python training and consulting

I conduct online courses on Python programming, Unix / Linux commands and shell scripting and SQL programming and database design , with course material and personal coaching sessions.

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