I have looked around for info on how to do this, just can't quite get it myself. Fairly new to Ruby and I'm building a gem. I can return a list of results from a website ok with Nokogiri.
The issue I'm having is how to take an input number and relate it to another piece of text from the website I'm scraping. So you pick a movie title by number from a list and then you return the relevant movie outline. Maybe I don't want to iterate through all the objects (again) at all.
This is what I'm looking at:
def menu
input = nil
while input != "exit"
input = gets.strip.downcase
if input.to_i < 24
#movies.each.with_index(1) do |movie, i|
puts "Description: #{movie.outline}"
end
end
end
end
So we create a variable for input. While the input is not the word exit and less than the number 24, we iterate through the movies and put the relevant one by index number. Currently putting ALL the movie outlines so I feel like I should ditch the iteration. I've tried a number of things around adding the input to movie.outline...
Any help or hints would be great!
It's hard to say for sure, but, are you maybe just trying to do this?
input = gets.to_i
if input < 24
movie = #movies[input]
puts "Description: #{movie.outline}"
end
Or something to that effect?
If you want to access an Array element, you use the [] notation (I'm assuming #movies is an Array, but if it's some other enumerable, you'll need to tell us what that is).
Related
I'm going to preface that I'm still learning ruby.
I'm writing a script to parse a .csv and identify possible duplicate records in the data-set.
I have a .csv file with headers, so I'm parsing the data so that I can access each row using a header title as such:
#contact_table = CSV.parse(File.read("app/data/file.csv"), headers: true)
# Prints all last names in table
puts contact_table['last_name']
I'm trying to iterate over each row in the table and identify if the last name I'm currently iterating over is similar to the next last name, but I'm having trouble doing this. I guess the way I'm handling it is as if it's an array, but I checked the type and it's a CSV::Row.
example (this doesn't work):
#contact_table.each_with_index do |c, i|
puts "first contact is #{c['last_name']}, second contact is #{c[i + 1]['last_name']}"
end
I realized this doesn't work like this because the table isn't an array, it's a CSV::Row like I previously mentioned. Is there any method that can achieve this? I'm really blanking right now.
My csv looks something like this:
id,first_name,last_name,company,email,address1,address2,zip,city,state_long,state,phone
1,Donalt,Canter,Gottlieb Group,dcanter0#nydailynews.com,9 Homewood Alley,,50335,Des Moines,Iowa,IA,515-601-4495
2,Daphene,McArthur,"West, Schimmel and Rath",dmcarthur1#twitter.com,43 Grover Parkway,,30311,Atlanta,Georgia,GA,770-271-7837
#contact_table should be a CSV::Table which is a collection of CSV::Rows so in this:
#contact_table.each_with_index do |c, i|
...
end
c is a CSV::Row. That's why c['last_name'] works. The problem is that here:
c[i + 1]['last_name']
you're looking at c (a single row) instead of #contact_table, if you said:
#contact_table[i + 1]['last_name']
then you'd get the next last name or, when c is the last row, an exception because #contact_table[i+1] will be nil.
Also, inside the iteration, c is the current (or (i+1)th) row and won't always be the first.
What is your use case for this? Seems like a school project?
I recommend for_each instead of parse (see this comparison). I would probably use a Set for this.
Create a Set outside of the scope of parsing the file (i.e., above the parsing code). Let's call it rows.
Call rows.include?(row) during each iteration while parsing the file
If true, then you know you have a duplicate
If false, then call rows.add(row) to add the new row to the set
You could also just fill your set with an individual value from a column that must be distinct (e.g., row.field(:some_column_name)), such as email or phone number, and do the same inclusion check for that.
(If this is for a real app, please don't do this. Use model validations instead.)
I would use #read instead of #parse and do something like this:
require 'csv'
LASTNAME_INDEX = 2
data = CSV.read('data.csv')
data[1..-1].each_with_index do |row, index|
puts "Contact number #{index + 1} has the following last name : #{row[LASTNAME_INDEX]}"
end
#~> Contact number 1 has the following last name : Canter
#~> Contact number 2 has the following last name : McArthur
I've flirted with learning web dev in the past and haven't had the time as I am a full time Business Student.
I started digging back in today and decided to take a break from the learning and practice what I've learned today by writing a simple program that allows the user to enter in their bills and will eventually calculate how much disposable income they have after their bills are paid each month.
My problem is that the program runs through perfectly, the loop is continuing/exiting when it should, but either the program is not storing the users input in the hash like I'm wanting it to or it's not displaying all the bills entered as it should. Here is my program:
# This program allows you to assign monthly payments
# to their respective bills and will automatically
# calculate how much disposable income you have
# after your bills are paid
# Prompts user to see if they have any bills to enter
puts "Do you have any bills you would like to enter, Yes or No?"
new_bill = gets.chomp.downcase
until new_bill == 'no'
# Creates a hash to store a key/value pair
# of the bill name and the respection payment amount
bills = {}
puts "Enter the bill name: "
bill_name = gets.chomp
puts "How much is this bill?"
pay_amt = gets.chomp
bills[bill_name] = pay_amt
puts "Would you like to add another bill, Yes or No?"
new_bill = gets.chomp.downcase
end
bills.each do |bill_name, pay_amt|
puts "Your #{bill_name} bill is $#{pay_amt}."
end
My questions are:
Is my hash set up properly to store the key/value pairs from the users input?
If not, how can I correct it?
I'm getting only the last bill that was entered by the user. I've tried several bills at a time but only getting the last entry.
As I stated, I'm a noob but I'm extremely ambitious to learn. I've referred to to the ruby docs on hashes to see if there is an error in my code but was able to locate a solution (still finding my way around ruby docs).
Any help is appreciated! Also, if you have any recommendations on ways I can make my code more efficient, could you point me in the direction where I can obtain the appropriate information to do so?
Thank you.
Edit:
The main question has been answered. This is a follow up question to the same program - I'm getting an error message budget_calculator.rb:35:in -': Hash can't be coerced into Float (TypeError)
from budget_calculator.rb:35:in'
From the following code (keep in mind of the program above) -
# Displays the users bills
bills_hash.each {|key,value| puts "Your #{key} bill is $#{value}."}
# Get users net income
puts "What is your net income?"
net_income = gets.chomp.to_f
#Calculates the disposable income of the user
disposable_income = net_income - bills_hash.each {|value| value}
puts disposable_income
I understand the error is appearing from this line of code:
disposable_income = net_income - bills_hash.each {|value| value}
I'm just not understanding why this is unacceptable. I'm trying to subtract all of the values in the hash (pay_amt) from the net income to derive the disposable income.
This is the part that's getting you:
bills = {}
You're resetting the hash every time the program loops. Try declaring bills at the top of the program.
As to your second question about bills_hash, it's not working because the program is attempting to subtract a hash from a float. You've got the right idea, but the way it's set up, it's not going to just subtract each key from the net_income in turn.
The return value of #each is the original hash that you were looping over. You can see this if you open IRB and type
[1,2,3].each {|n| puts n}
The block is evaluated for each element of the list, but the final return value is the original list:
irb(main):007:0> [1,2,3].each {|n| puts n}
1
2
3
=> [1, 2, 3] # FINAL RETURN VALUE
So according to the order of operations, your #each block is iterating, then returning the original bills_hash hash, and then trying to subtract that hash from net_income, which looks like this (assuming my net_income is 1000):
1000 - {rent: 200, video_games: 800}
hence the error.
There are a couple ways you could go about fixing this. One would be to sum all of the values in bills_hash as its own variable, then subtract that from the net_income:
total_expenditures = bills_hash.values.inject(&:+) # sum the values
disposable_income = net_income - total_expenditures
Using the same #inject method, this could also be done in one function call:
disposable_income = bills_hash.values.inject(net_income, :-)
# starting with net_income, subtract each value in turn
See the documentation for Enumerable#inject.
It's a very powerful and useful method to know. But make sure you go back and understand how return values work and why the original setup was raising an exception.
Now i am making a web application (Online word learning) that allow user to choose the correct meaning of the word. When they click start, it will select randomly one word from the database and show to the user. After the user choose the answer, it will go to the next question.
Please see the image below:
If i use, Word.order("rand()").limit(1), i wonder can the word will be repeated with the last selected word?
With the app as in the image above, any better ideas to solve this problem?
I would add the following scopes to the model (depends on the database you are using):
# in app/models/word.rb
# 'RANDOM' works with postgresql and sqlite, whereas mysql uses 'RAND'
scope :random, -> { order('RAND()') }
scope :without, ->(ids) { where.not(id: ids) }
With that scopes you can write the following query in your controller:
#word = Word.random.without(params[:last_ids]).limit(1)
When you want to load new random elements in the view, just add the ids of the current words to the request. This ensures that this ids (params[:last_ids]) are not randomly choosen.
Long story short, in order not to repeat yourself, you have to store those words somewhere. Either the ones that are yet to be shown, or the ones that have been already displayed. And If I were you I would go one of the following routes:
Fetch all the words before starting the quiz and randomize them. This could be something like:
session[:words] = Word.order("RAND()").select(:id).take(10)
Or even better by defining a scope for your random words:
class Word < ActiveRecord::Base
# ...
scope :random_quiz, -> { order("RAND()").take(10).pluck(:id) }
# ...
end
# ... in the controller when the quiz is getting started:
session[:words] = Word.random_quiz
# ... in the controller when you want to show the word:
new_word = Word.find(sessions[:words].pop)
As ORDER BY RAND() is a very expensive operation, this might make sense. And then you just pop the word ID's one by one by using session[:words].pop and present the questions.
This way it will guarantee that you won't repeat the words in the quiz and give you pretty optimal performance.
Fetch words one by one as you're progressing with giving out the questions and save the ones you've already asked about.
class Word < ActiveRecord::Base
# ...
def self.random_word(exclusions)
eligible = where('id NOT IN (?)', exclusions)
eligible.offset(rand(0..eligible.count)).take!(1)
end
# ..
end
# ... in the controller when you need a new word:
session[:words_shown] ||= [ ]
new_word = Word.random_word(session[:words_shown])
# mark the word as shown:
session[:words_shown].push(new_word.id)
You might have noticed the weird way of getting a random record in the second example. It turns out to be more efficient as it generates the following query:
SELECT * FROM words OFFSET _random_number_ LIMIT 1
Instead of:
SELECT * FROM words ORDER BY RAND() LIMIT 1
The first one is just an ordinary select, while the second one requires unindexed sorting by RAND() of the entire table before giving you that random result. Turns out to be the former is almost tenfold faster than the latter.
Hope that makes sense!
Arrays have always been my downfall in every language I've worked with, but I'm in a situation where I really need to create a dynamic array of multiple items in Rails (note - none of these are related to a model).
Briefly, each element of the array should hold 3 values - a word, it's language, and a translation into English. For example, here's what I'd like to do:
myArray = Array.new
And then I'd like to push some values to the array (note - the actual content is taken from elsewhere - although not a model - and will need to be added via a loop, rather than hard coded as it is here):
myArray[0] = [["bonjour"], ["French"], ["hello"]]
myArray[1] = [["goddag"], ["Danish"], ["good day"]]
myArray[2] = [["Stuhl"], ["German"], ["chair"]]
I would like to create a loop to list each of the items on a single line, something like this:
<ul>
<li>bonjour is French for hello</li>
<li>goddag is Danish for good day</li>
<li>Stuhl is German for chair</li>
</ul>
However, I'm struggling to (a) work out how to push multiple values to a single array element and (b) how I would loop through and display the results.
Unfortunately, I'm not getting very far at all. I can't seem to work out how to push multiple values to a single array element (what normally happens is that the [] brackets get included in the output, which I obviously don't want - so it's possibly a notation error).
Should I be using a hash instead?
At the moment, I have three separate arrays, which is what I've always done, but I don't particularly like - that is, one array to hold the original word, one array to hold the language, and a final array to hold the translation. While it works, I'm sure this is a better approach - if I could work it out!
Thanks!
Ok, let's say you have the words you'd like in a CSV file:
# words.csv
bonjour,French,hello
goddag,Danish,good day
stuhl,German,chair
Now in our program we can do the following:
words = []
File.open('words.csv').each do |line|
# chomp removes the newline at the end of the line
# split(',') will split the line on commas and return an array of the values
# We then push the array of values onto our words array
words.push(line.chomp.split(','))
end
After this code is executed, the words array had three items in it, each item is an array that is based off of our file.
words[0] # => ["bonjour", "French", "hello"]
words[1] # => ["goddag", "Danish", "good day"]
words[2] # => ["stuhl", "German", "chair"]
Now we want to display these items.
puts "<ul>"
words.each do |word|
# word is an array, word[0], word[1] and word[2] are available
puts "<li>#{word[0]} is #{word[1]} for #{word[2]}</li>"
end
puts "</ul>"
This gives the following output:
<ul>
<li>bonjour is French for hello</li>
<li>goddag is Danish for good day</li>
<li>stuhl is German for chair</li>
</ul>
Also, you didn't ask about it, but you can access part of a given array by using the following:
words[0][1] # => "French"
This is telling ruby that you want to look at the first (Ruby arrays are zero based) element of the words array. Ruby finds that element (["bonjour", "French", "hello"]) and sees that it's also an array. You then asked for the second item ([1]) of that array and Ruby returns the string "French".
You mean something like this?
myArray.map{|s|"<li>#{[s[0],'is',s[1],'for',s[2]].join(" ")}</li>"}
Thanks for your help guys! I managed to figure a solution out based on your advice
For the benefit of anyone else who stumbles across this problem, here's my elided code. NB: I use three variables called text, language and translation, but I suppose you could replace these with a single array with three separate elements, as Jason suggests above.
In the Controller (content is being added via a loop):
#loop start
my_array.push(["#{text}", "#{language}", "#{translation}"])
#loop end
In the View:
<ul>
<% my_array.each do |item| %>
<li><%= item[0] # 0 is the original text %> is
<%= item[1] # 1 is the language %> for
<%= item[2] # 2 is the translation %></li>
<% end %>
</ul>
Thanks again!
I'm using Mongoid to work with MongoDB. Everything is fine, I like it very much and so on. In my blog application (posts controller, index action) I have this code:
#posts = Post.without(:comments)
#posts = #posts.my_search(params[:s]) if params[:s]
#posts = #posts.order_by([:created_at, :desc])
#posts = #posts.where(:pid.lt => params[:p].to_i+1) if params[:p]
#posts = #posts.limit(items_per_page+1)
The part with "where" is implementation of my own pagination method (allows to page results in one direction only, but without skip(), what I consider a plus). Now, there are few small problems that make me feel uncomfortable:
For my pagination to work I need to get the last post within that limit. But when I do #posts.last I'm getting last document of the whole query without limit. Ok, this is strange, but not a big problem. Other than that, query results act like almost-ordinary-array, so at this moment I'm getting the last element with #posts.pop (funny, but it doesn't remove any documents) or #posts.fetch(-1)
I have a feeling that this isn't "right way" and there mush be something more elegant. Also
#posts.count generates second query exactly the same as first one (without limit) but with "count" only and I don't like it.
If I make the last line look like
#posts = #posts.limit(items_per_page+1).to_ary
to convert query results into array, everything generates only one query (good), but now #posts.count stops reporting what I need (total amount of documents without limit applied) and behaves exactly like #posts.size - it returns items_per_page+1 or less (bad).
So, here are my questions:
1) What is a "correct" way to get the last document of query results within given limit?
2) How to get total amount of documents with given conditions applied without generating additional query?
UPD:
3) #posts.first generates additional query, how to prevent it and just get first document before I iterate all documents?
Getting the last document:
Post.last
Getting last document with some other queries:
Post.order_by([:created_at, :desc]).last
Getting total number documents:
Post.order_by([:created_at, :desc]).count
Recommendation: Just use the built in pagination
#posts = Post.limit(10).paginate(:page=>pararms[:page])
later:
<%= will_paginate #posts %>
Regarding the additional queries -- mongoid lazy loads everything:
#posts = Post.all #no query has been run yet
#posts.first #Ok, a query has finally been run because you are accessing the objects