- 2.1 Representing Ordinary Strings
- 2.2 Representing Strings with Alternate Notations
- 2.3 Using Here-Documents
- 2.4 Finding the Length of a String
- 2.5 Processing a Line at a Time
- 2.6 Processing a Byte at a Time
- 2.7 Performing Specialized String Comparisons
- 2.8 Tokenizing a String
- 2.9 Formatting a String
- 2.10 Using Strings As IO Objects
- 2.11 Controlling Uppercase and Lowercase
- 2.12 Accessing and Assigning Substrings
- 2.13 Substituting in Strings
- 2.14 Searching a String
- 2.15 Converting Between Characters and ASCII Codes
- 2.16 Implicit and Explicit Conversion
- 2.17 Appending an Item Onto a String
- 2.18 Removing Trailing Newlines and Other Characters
- 2.19 Trimming Whitespace from a String
- 2.20 Repeating Strings
- 2.21 Embedding Expressions Within Strings
- 2.22 Delayed Interpolation of Strings
- 2.23 Parsing Comma-Separated Data
- 2.24 Converting Strings to Numbers (Decimal and Otherwise)
- 2.25 Encoding and Decoding rot13 Text
- 2.26 Encrypting Strings
- 2.27 Compressing Strings
- 2.28 Counting Characters in Strings
- 2.29 Reversing a String
- 2.30 Removing Duplicate Characters
- 2.31 Removing Specific Characters
- 2.32 Printing Special Characters
- 2.33 Generating Successive Strings
- 2.34 Calculating a 32-Bit CRC
- 2.35 Calculating the MD5 Hash of a String
- 2.36 Calculating the Levenshtein Distance Between Two Strings
- 2.37 Encoding and Decoding base64 Strings
- 2.38 Encoding and Decoding Strings (uuencode/uudecode)
- 2.39 Expanding and Compressing Tab Characters
- 2.40 Wrapping Lines of Text
- 2.41 Conclusion
This chapter is from the book
This chapter is from the book
This chapter is from the book
2.27 Compressing Strings
The Zlib library provides a way of compressing and decompressing strings and files.
Why might we want to compress strings in this way? Possibly to make database I/O faster, to optimize network usage, or even to obscure stored strings so that they are not easily read.
The Deflate and Inflate classes have class methods named deflate and inflate, respectively. The deflate method (which obviously compresses) has an extra parameter to specify the style of compression. The styles show a typical trade-off between compression quality and speed; BEST_COMPRESSION results in a smaller compressed string, but compression is relatively slow; BEST_SPEED compresses faster but does not compress as much. The default (DEFAULT_COMPRESSION) is typically somewhere in between in both size and speed.
require 'zlib'
include Zlib
long_string = ("abcde"*71 + "defghi"*79 + "ghijkl"*113)*371
# long_string has 559097 characters
s1 = Deflate.deflate(long_string,BEST_SPEED) # 4188 chars
s3 = Deflate.deflate(long_string) # 3568 chars
s2 = Deflate.deflate(long_string,BEST_COMPRESSION) # 2120 chars
Informal experiments suggest that the speeds vary by a factor of two, and the compression amounts vary inversely by the same amount. Speed and compression are greatly dependent on the contents of the string. Speed of course also is affected by hardware.
Be aware that there is a "break-even" point below which it is essentially useless to compress a string (unless you are trying to make the string unreadable). Below this point, the overhead of compression may actually result in a longer string.