🗜 txt cmprssn
06 Feb 2017🎯 Learning Targets
AP I can analyze how data representation, storage, security, and transmission of data involve computational manipulation of information.
AP I can use computers to process information, find patterns, and test hypotheses about digitally processed information to gain insight and knowledge.
I can develop a strategy (heuristic algorithm) for compressing text.
Do now
SMH. LOL.
Why do we use abbreviations in texts?
🗜Text Compression
We “compress” txt 2 save time. Computers do it too, to save time and space.
Compression: represent data with fewer bits. Why might that be useful? Think about the Bytes & File Sizes research that you did.
Decode Text
I wish I was a little bit taller
I wish I was a baller
I wish I had a girl who looked good, I would call her
I wish I had a rabbit in a hat with a bat
And a six four Impala
| Symbol | Value |
|---|---|
| ☀ | I_ |
| ☂ | wish_ |
| ☃ | aller_ |
| ☄ | was_a_ |
| ★ | had_a_ |
| ☆ | _a_ |
☀☂☀☄little_bit_t☃☀☂☀☄b☃☀☂☀★girl_who_looked_good,☀would_call_her☀☂☀★rabbit_in☆hat_with☆bat_And☆six_four_Impala
Original text size: 172 bytes
Compressed text size: 111 bytes
So we saved 61 bytes, right?
WRONG
We also need to let our recipient decode our message.
Dictionary size: 34 bytes
Total: 145 bytes
Compression: 27 bytes, or 15.75% !!
🗜 txt cmprssn
Choose a text from English class and try to compress it.
Your goal is to get the highest compression rate. Keep note of your strategy.
What’s the best compression scheme?
Heuristic
a problem solving approach (algorithm) to find a satisfactory solution where finding an optimal or exact solution is impractical or impossible.
What kind of scenarios is our heuristic good for?
You could very easily create a “compressed” file that’s BIGGER than the original!
Questions
- What did all groups’ processes for compression have in common?
- Will following this process always lead to the same compression?
- If you send the compressed poem, would your friend will be able to read it? Why is the dictionary important?
- Why do you want to compress anything? What’s the point?
Case Study
A simple message has been compressed below:
What was the original message?
What was the compression rate?