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Jay Godse [Jay Godse] - Ruby Data Processing: Using Map, Reduce, and Select

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Book:
Ruby Data Processing: Using Map, Reduce, and Select
Author:
Jay Godse Jay Godse
Publisher:
Apress
Genre:
Books / Computer
Year:
2018
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Ruby Data Processing: Using Map, Reduce, and Select: summary, description and annotation

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Gain the basics of Rubys map, reduce, and select functions and discover how to use them to solve data-processing problems. This compact hands-on book explains how you can encode certain complex programs in 10 lines of Ruby code, an astonishingly small number. You will walk through problems and solutions which are effective because they use map, reduce, and select. As you read Ruby Data Processing, type in the code, run the code, and ponder the results. Tweak the code to test the code and see how the results change.
After reading this book, you will have a deeper understanding of how to break data-processing problems into processing stages, each of which is understandable, debuggable, and composable, and how to combine the stages to solve your data-processing problem. As a result, your Ruby coding will become more efficient and your programs will be more elegant and robust.
What You Will Learn

Discover Ruby data processing and how to do it using the map, reduce, and select functions
Develop complex solutions including debugging, randomizing, sorting, grouping, and more
Reverse engineer complex data-processing solutions

Who This Book Is For
Those who have at least some prior experience programming in Ruby and who have a background and interest in data analysis and processing using Ruby.

Jay Godse [Jay Godse]: author's other books

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Jay Godse 2018

Jay Godse Ruby Data Processing

1. Basic Ruby

Jay Godse 1

(1)

Kanata, Ontario, Canada

This section will acquaint or refresh you with basic ways to use the Ruby command line, as well as some relevant Ruby coding.

If you are comfortable programming in Ruby and understand the Ruby Enumerable Library reasonably well, you can skip this section.

The Command Line

After you install Ruby, you can fire up the interactive command line in Windows, Linux, or Mac OSX. Im using Windows.

C:\> irb

irb(main):001:0>

For brevity, I wont write the full irb prompt every time.

You can execute Ruby statements line by line. The value returned by each expression is preceded by .

irb> a = 4

=> 4

irb> a

=> 4

irb> a + 7

=> 11

You can choose to put multiple statements on one line, separated by a semicolon.

irb> list = ["one", "two","three"];1

=>1

irb> list

=>["one", "two", "three"]

You can also have a statement that spans multiple lines.

irb> [2,3,4,5].each do |n|

irb> if n%2==0

irb> puts "even"

irb> else

irb> puts "odd"

irb> end

=> "even"

=> "odd"

=> "even"

=> "odd"

You can put the code into a file called sample.rb , located in the same directory or folder from which you ran irb .

1 [2,3,4,5].each do |n|

2 if n%2 == 0

3 puts "even"

4 else

5 puts "odd"

6 end

7 end

Then, with irb :

irb> load "sample.rb"

irb> end

=> "even"

=> "odd"

=> "even"

=> "odd"

irb>

You could also copy the code block from your text editor and paste it directly into your command line and get the same result, as long as you use only spaces for indentation. (Using tabs for indentation will work fine if you load the file from the command prompt, but if you paste tabs directly into irb , it will generate errors).

You can either type the code samples from this book into irb directly or type them into a text editor and then load the file as just shown.

Object Scope

When you are in a Ruby program, the general method of executing a method f on an object obj is as follows:

obj.f

That is true whether you are in a Ruby program or the command line. When code is in the main program file, or in the irb command-line interpreter, there is an implied context for many functions, such as puts . That is why you can do this:

puts "Hello world"

You dont need to specify a class to qualify puts , because puts is a method of the underlying context object.

String

Strings are basic constructs in all languages. Lets look at a few basic operations used in this book. Try them out on the irb command line for yourself.

length or size

This yields the size of the string.

downcase

This converts all letters to lowercase.

upcase

This converts all letters to uppercase.

capitalize

This capitalizes the first letter of a string.

split()

This searches a substring for the argument string and splits the string into a array comprising substrings on both sides of the split argument, while the substring of the split argument is discarded. If there are no matches, an array is returned with the whole string:
irb> base_string = "abc def ghi"
irb> base_string.split(" ")
=> ["abc","def","ghi"]
irb> base_string.split(" ")
=> ["abc def","ghi"]
irb> base_string.split(" d")
=> ["abc","ef ghi"]
irb> base_string.split("efghi")
=> ["abc def ghi"]

join()

This joins each element of an array of strings with the string in the join argument as the separator.
irb> stringlist = ["This", "is", "a", "sentence"]
irb> stringlist.join(" ")
=> "This is a sentence"
irb> stringlist.join(",")
=> "This,is,a,sentence"
irb> stringlist.join(" A SPACE ")
=> "This A SPACE is A SPACE a A SPACE sentence "

string interpolation

This lets you define a string template with parameters. The string #{} gives you a place to put a variable.
irb> first = "Jack"; last = "Black"
irb> full_name = " #{ first } #{ last } "
=> "Jack Black"
This is especially useful for iterating over a list:
irb> smith_brothers = ["Terry", "Jerry", "Harry"]
irb> smith_brothers.each{|brother| puts " #{ brother } Smith"}
Terry Smith
Jerry Smith
Harry Smith
=> ["Terry", "Jerry", "Harry"]
C/C++ programmers will recognize string interpolation as being similar to the sprintf function in the C standard library.

Array

Arrays in Ruby are like arrays in other languages. They are a collection of things indexed by a whole number (e.g., 0,1,2,). In Ruby, an array can contain any Ruby object at an index. Array indices in Ruby start at .

Arrays implement the Ruby Enumerable interface, so they will have key methods such as each , map , reduce , select , and others.

Special Methods

compact()

This method on an array gets rid of nil members. For example:
irb> [1, nil ,2, nil , nil ,3, nil ,[]].compact
=> [1,2,3,[]]

flatten()

This method gets rid of inner arrays to an arbitrary depth. It is often useful when dealing with nested map and reduce statements. For example:
irb> [[1,[2,3]],4,[5,6]].flatten
=> [1,2,3,4,5,6]

push()

This method pushes an element onto the end of an array and returns a new array. For example:
irb> [1,2,3,4,5].push(666)
=> [1,2,3,4,5,666]

pop

This method removes the last element of an array and returns that element and returns a new array. For example:
irb> the_array = [1,2,3,4,5]
irb> tail = the_array.pop
irb> tail
=> 5
irb> the_array
=> [1, 2, 3, 4]

unshift()

This method pushes an element onto the beginning of an array and returns a new array. For example:
irb> the_array = [1,2,3,4,5]
irb> the_array.unshift(666)
=> [666, 1, 2, 3, 4, 5]

shift

This method removes the first element of an array and returns that element and modifies the old array. For example:
irb> the_array = [1,2,3,4,5]
irb> head = the_array.shift
irb> head
=> 1
irb> the_array
=> [2, 3, 4, 5]

Hash

Another term for hash is an associative array, or even a dictionary, Hashes are indexed by a key object, and there is a value (another object) for each key object.

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