Lesson content is currently in draft form.

We’ve run through a fair number of concepts and code but really haven’t done anything we couldn’t do (and do faster) with a web browser, such as look up a Twitter user’s number of followers, or how many people retweeted his/her most recent tweet.

If you’re a pretty fast copy-and-paster, you might be able to outpace a mouse-clicker by copying-and-pasting the tweet-data-fetching routines over and over, which is not a bad accomplishment.

But we can do much better than that.

Make a simple goal

In programming, you’ll get more return out of every line of code when you break things down into simple tasks.

In the last chapter, what was one of our goals? To print out the text of a tweet.

Repeat that step across a collection

The code for printing out one tweet’s text is the same as it is for any other given tweet. The only difference is the reference to each tweet, i.e. its address in an array.

each

Ruby collections have many useful methods, but the one we’ll use the most is each. In a nutshell, each lets us loop through a collection and perform a method on each member of that collection.

On a simple array:

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['a', 'b', 'c'].each do |some_item|
  puts some_item.upcase
end

#=>
A
B
C

Without getting into the nitty-gritty, think of what is between the do and the end as the routine done on each some_item.

What is some_item? In this syntax, the value in the straight pipe-characters is the variable name used to reference a member of the collection.

If you think of each as looping through the collection and doing something on each member of the collection, then some_item (which we could name anything we want, as if it were a variable) points to the member of the current iteration.

There are other variations of the each method. For a Hash object, you could use each_pair:

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my_hash = {'a'=>'alpha', 'b'=>'beta', 'c'=>'charlie'}

my_hash.each_pair do |k,v|
  puts k.to_s + " is the key for: " + v.to_s
end

#=>
a is the key for: alpha
b is the key for: beta
c is the key for: charlie

Exercise

1. Using the each method, loop through the array of tweets from the last lesson and print out the contents of the text.

2. Using the each method again, loop through the tweets and print the length of their text.

3. Same procedure above, but use it to calculate the average length of a tweet.

4. Using the each method again, loop through and print out every attribute of each tweet.

Answer

To get the tweets in an array:

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require 'rubygems'
require 'json'
require 'httparty'

screenname = "ChuckGrassley"


url = File.join( "http://nottwitter.danwin.com",
  "statuses",
  screenname,
  1.to_s,
  "user_timeline.json" ) 

json_str = HTTParty.get(url).body
tweets_obj = JSON.parse(json_str)

1. Printing out text:

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tweets_obj.each do |tweet|
  puts tweet['text']
end

Note: if you are using irb, the result of each each invocation will spit out the entire contents of the collection. This is irb’s normal behavior, to return the value of each method call after you hit Enter. It’s slightly annoying and means you’ll have to scroll up a bit to find the output you want. Or you could append a trivial line of code after the keyword end, on the same line with a semi-colon as separation. Like so:

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tweets_obj.each do |tweet|
  puts tweet['text']
end; puts "done with each"

1. Printing out the length of each tweet

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tweets_obj.each do |tweet|
  puts tweet['text'].length
end

1. Printing out the average length the tweets

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total_length = 0
tweets_obj.each do |tweet|
  total_length = total_length + tweet['text'].length
end

puts total_length / tweets_obj.length

1. Printing out the attributes of each tweet

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tweets_obj.each do |tweet|
  tweet.each_pair do |key, val|
      puts key.to_s + " --> " + val.to_s
  end
end