I have the following code which takes a CSV file and feed it into a hash. Here I want to list all the names of songs for a specific genre. Like, all the "Western" songs. This code only gives me one song for a specific genre. Does anyone have suggestions on how I can get it to show all the Western songs (for example)
def self.musicGenre()
puts "Ballad,Blues,Bluegrass,Popular,Western"
require 'csv'
#musicGenreHash={} #create the hash for musicName, blank
CSV.foreach('musiclist.txt')do |row|
name,genre,composer,location = row
#musicGenreHash[genre]=name
end
def self.genre(songGenreChoice)
#musicGenreHash[songGenreChoice]
end
puts "Please type in the genre of your choice:"
songGenreChoice=gets.chomp
puts "Thesearethesongsavailable in the#{songGenreChoice} genre:"+genre("#{songGenreChoice}").inspect
end #musicGenre
You are storing only one value against a genre. You need to modify your code so that values in the hash are array, and you collect the names of all songs belonging to particular genre in that array.
Change
#musicGenreHash[genre]=name
to
#musicGenreHash[genre] = (#musicGenreHash[genre] || []) << name
Related
I am trying to take an existing CSV file, add a fourth row to it, and then iterate through the second and third row to create the fourth rows values. Using Ruby I've created hashes where the headers are the keys and the column values are the hash values (ex: "id"=>"1", "new_fruit" => "apple")
My practice CSV file looks like this:practice csv file image
My goal is to create a fourth column: "brand_new" (which I was able to do) and then add values to it by concatenating the values from the second and third row (which I am stuck on). At the moment I just have a placement value (x) for the fourth columns values so I could see if adding the fourth column to the hash actually worked: Results with x = 1
Here is my code:
require 'csv'
def self.import
table = []
CSV.foreach(File.path("practice.csv"), headers: true) do |row|
table.each do |row|
row["brand_new"] = full_name
end
table << row.to_h
end
table
end
def full_name
x = 1
return x
end
# Add another col, row by row:
import.each do |row|
row["brand_new"] = full_name
end
puts import
Any suggestions or guidance would be much appreciated. Thank you.
Simplified your code a bit. I read the file first, then iterate about the read content.
Note: Change col_sep to comma or delete it to use the default if needed.
require "csv"
def self.import
table = CSV.read("practice.csv", headers: true , col_sep: ";")
table.each do |row|
row["brand_new"] = "#{row["old_fruit"]} #{row["new_fruit"]}"
end
puts table
end
I use the read method to read the CSV file content. It allows you to directly access the column/cell values.
Line 7 shows how to concatenate the column values as string:
"#{row["old_fruit"]} #{row["new_fruit"]}"
Refer to this old SO post and the CSV Ruby docs to learn more about working with CSV files.
So i got in big troubles with this exam at university because i am stuck with a part in my ruby code. I just can't figure out how
" If the user presses 2 the program shall ask for an employee number and afterwards search for the employee. If the program finds it, then print and if not, print a message saying it doesn’t have it."
My problem is that i'm not sure that the information is saved corectly in the file. But if it is... the problem is that the hash i've made isn't taking the information that already is saved in the file and only works with the information it has received last.
puts "Insert Registration number \n"
search = gets.chomp
hash = Hash.new()
hash = {(regnr) => (name)}
hash.each do |key, value|
puts "#{key} \t | \t #{value}"
end
search =~ File.new("employees.txt", "r")
if hash.has_key? (search)
print "The person you were looking for is "
puts hash [search]
else
puts "He isn't one of our employees"
end
I have to tell you guys that i have only been coding for one month and the school isn't taking me easy...
I'd recommend using yaml. Take a look around the web for some examples on using YAML. It's a structured markup that can represent hashes. You can easily dump and load simple ruby objects like hashes and arrays.
require 'yaml'
parsed = begin
employee_hash = YAML.load(File.open("employees.yml"))
rescue ArgumentError => e
puts "Could not parse YAML: #{e.message}"
end
This is my code, which is supposed to hash the 2 columns in fotoFd.csv and then save the hashed columns in a separate file, T4Friendship.csv:
require "csv"
arrayUser=[]
arrayUserUnique=[]
arrayFriends=[]
fileLink = "fotoFd.csv"
f = File.open(fileLink, "r")
f.each_line { |line|
row = line.split(",");
arrayUser<<row[0]
arrayFriends<<row[1]
}
arrayUserUnique = arrayUser.uniq
arrayHash = []
for i in 0..arrayUser.size-1
arrayHash<<arrayUser[i]
arrayHash<<i
end
hash = Hash[arrayHash.each_slice(2).to_a]
array1 =hash.values_at *arrayUser
array2 =hash.values_at *arrayFriends
fileLink = "T4Friendship.csv"
for i in 0..array1.size-1
logfile = File.new(fileLink,"a")
logfile.print("#{array1[i]},#{array2[i]}\n")
logfile.close
end
The first columns contains users, and the second column contains their friends. So, I want it to produce something like this in the T4Friendship.csv:
1 2
1 4
1 10
1 35
2 1
2 8
2 11
3 28
3 31
...
The problem is caused by the splat expansion of a large array. The splat * can be used to expand an array as a parameter list. The parameters are passed on the stack. If there are too many parameters, you'll exhaust stack space and get the mentioned error.
Here's a quick demo of the problem in irb that tries to splat an array of one million elements when calling puts:
irb
irb(main):001:0> a = [0] * 1000000; nil # Use nil to suppress statement output
=> nil
irb(main):002:0> puts *a
SystemStackError: stack level too deep
from /usr/lib/ruby/1.9.1/irb/workspace.rb:80
Maybe IRB bug!
irb(main):003:0>
You seem to be processing large CSV files, and so your arrayUser array is quite large. Expanding the large array with the splat causes the problem on the line:
array1 =hash.values_at *arrayUser
You can avoid the splat by calling map on arrayUser, and converting each value in a block:
array1 = arrayUser.map{ |user| hash[user] }
Suggested Code
Your code appears to map names to unique ID numbers. The output appears to be the same format as the input, except with the names translated to ID numbers. You can do this without keeping any arrays around eating up memory, and just use a single hash built up during read, and used to translate the names to numbers on the fly. The code would look like this:
def convertCsvNamesToNums(inputFileName, outputFileName)
# Create unique ID number hash
# When unknown key is lookedup, it is added with new unique ID number
# Produces a 0 based index
nameHash = Hash.new { |hash, key| hash[key] = hash.size }
# Convert input CSV with names to output CSV with ID numbers
File.open(inputFileName, "r") do |inputFile|
File.open(outputFileName, 'w') do |outputFile|
inputFile.each_line do |line|
# Parse names from input CSV
userName, friendName = line.split(",")
# Map names to unique ID numbers
userNum = nameHash[userName]
friendNum = nameHash[friendName]
# Write unique ID numbers to output CSV
outputFile.puts "#{userNum}, #{friendNum}"
end
end
end
end
convertCsvNamesToNums("fotoFd.csv", "T4Friendship.csv")
Note: This code assigns ID numbers to user and friends, as they are encountered. Your previous code assigned ID numbers to users only, and then looked up the friends after. The code I suggested will ensure friends are assigned ID numbers, even if they never appeared in the user list. The numerical ordering will different slightly from what you supplied, but I assume that is not important.
You can also shorten the body of the inner loop to:
# Parse names from input, map to ID numbers, and write to output
outputFile.puts line.split(",").map{|name| nameHash[name]}.join(',')
I thought I'd include this change separately for readability.
Updated Code
As per your request in the comments, here is code that gives priority to the user column for ID numbers. Only once the first column is completely processed will ID numbers be assigned to entries in the second column. It does this by first passing over the input once, adding the first column to the hash, and then passing over the input a second time to process it as before, using the pre-prepared hash from the first pass. New entries can still be added in the second pass in the case where the friend column contains a new entry that doesn't exist anywhere in the user column.
def convertCsvNamesToNums(inputFileName, outputFileName)
# Create unique ID number hash
# When unknown key is lookedup, it is added with new unique ID number
# Produces a 0 based index
nameHash = Hash.new { |hash, key| hash[key] = hash.size }
# Pass over the data once to give priority to user column for ID numbers
File.open(inputFileName, "r") do |inputFile|
inputFile.each_line do |line|
name, = line.split(",") # Parse name from line, ignore the rest
nameHash[name] # Add name to unique ID number hash (if it doesn't already exist)
end
end
# Convert input CSV with names to output CSV with ID numbers
File.open(inputFileName, "r") do |inputFile|
File.open(outputFileName, 'w') do |outputFile|
inputFile.each_line do |line|
# Parse names from input, map to ID numbers, and write to output
outputFile.puts line.split(",").map{|name| nameHash[name]}.join(',')
end
end
end
end
convertCsvNamesToNums("fotoFd.csv", "T4Friendship.csv")
I've been trying to find an answer for a little while now, and I'm not sure if I'm asking the wrong questions, but I've had no luck so far.
I have an array generated from querying an SQLite table. I also have an array of times generated from a csv file. I am trying to pull the time[0] (an id number) and check if it exists in the array from the SQL table
array = []
SQLite3::Database.new("t.db") do |db|
db.execute ("SELECT t FROM ts") do |row|
array << row
end
end
times = CSV.read('times1.csv')
times.each do |time|
#puts "This is the trip id: #{time[0]}"
if array.include? time[0]
puts time[0]
end
end
When I do this, I get no results. I know for a fact that there should be a few matches. When I try to iterate over the array like:
array.each do |row|
if row = 2345
puts "Match found"
end
end
Here is the strange part that has really stumped me. I know that 2345 only comes up once or twice in the array, however when I run this code, it seems as though it prints "Match found" for every element (like 5,000 times it says "Match found"). I feel like something is wrong with the array generated from the SQLite but I can't for the life of me figure it out.
Any ideas? Thanks.
In here:
db.execute ("SELECT t FROM ts") do |row|
your row is an array whose sole element is the t you're after. That means that you end up with an array-of-arrays in array rather than an array of numbers and of course your array.include? time[0] check fails because array only contains other arrays.
You probably want to say:
array << row[0]
to collect the t values in array.
Is there a way to dynamically create arrays in Ruby? For example, let's say I wanted to loop through an array of books as input by a user:
books = gets.chomp
The user inputs:
"The Great Gatsby, Crime and Punishment, Dracula, Fahrenheit 451,
Pride and Prejudice, Sense and Sensibility, Slaughterhouse-Five,
The Adventures of Huckleberry Finn"
I turn this into an array:
books_array = books.split(", ")
Now, for each book the user input, I'd like to Ruby to create an array. Pseudo-code to do that:
x = 0
books_array.count.times do
x += 1
puts "Please input weekly sales of #{books_array[x]} separated by a comma."
weekly_sales = gets.chomp.split(",")
end
Obviously this doesn't work. It would just re-define weekly_sales over and over again. Is there a way to achieve what I'm after, and with each loop of the .times method create a new array?
weekly_sales = {}
puts 'Please enter a list of books'
book_list = gets.chomp
books = book_list.split(',')
books.each do |book|
puts "Please input weekly sales of #{book} separated by a comma."
weekly_sales[book] = gets.chomp.split(',')
end
In ruby, there is a concept of a hash, which is a key/value pair. In this case, weekly_sales is the hash, we are using the book name as the key, and the array as the value.
A small change I made to your code is instead of doing books.count.times to define the loop and then dereference array elements with the counter, each is a much nicer way to iterate through a collection.
The "push" command will append items to the end of an array.
Ruby Docs->Array->push
result = "The Great Gatsby, Crime and Punishment, Dracula, Fahrenheit 451,
Pride and Prejudice, Sense and Sensibility, Slaughterhouse-Five,
The Adventures of Huckleberry Finn".split(/,\s*/).map do |b|
puts "Please input weekly sales of #{b} separated by a comma."
gets.chomp.split(',') # .map { |e| e.to_i }
end
p result
Remove the comment if you would like the input strings converted to numbers
One way or another you need a more powerful data structure.
Your post gravitates toward the idea that weekly_sales would be an array paralleling the books array. The drawback of this approach is that you have to maintain the parallelism of these two arrays yourself.
A somewhat better solution is to use the book title as a key to hash of arrays, as several answers have suggested. For example: weekly_sales['Fahrenheit 451'] would hold an array of sales data for that book. This approach hinges on the uniqueness of the book titles and has other drawbacks.
A more robust approach, which you might want to consider, is to bundle together each book's info into one package.
At the simplest end of the spectrum would be a list of hashes. Each book would be a self-contained unit along these lines:
books = [
{
'title' => 'Fahrenheit 451',
'sales' => [1,2,3],
},
{
'title' => 'Slaughterhouse-Five',
'sales' => [123,456],
},
]
puts books[1]['title']
At the other end of the spectrum would be to create a proper Book class.
And an intermediate approach would be to use a Struct (or an OpenStruct), which occupies a middle ground between hashes and full-blown objects. For example:
# Define the attributes that a Book will have.
Book = Struct.new(:title, :weekly_sales)
books = []
# Simulate some user input.
books_raw_input = "Fahrenheit 451,Slaughterhouse-Five\n"
sales_raw_input = ['1,2,3', '44,55,66,77']
books_raw_input.chomp.split(',').each do |t|
ws = sales_raw_input.shift.split(",")
# Create a new Book.
books.push Book.new(t, ws)
end
# Now each book is a handy bundle of information.
books.each do |b|
puts b.title
puts b.weekly_sales.join(', ')
end
Are you happy to end up with an array of arrays? In which this might be useful:
book_sales = books_array.collect do |book|
puts "Please input weekly sales of #{books_array[0]} separated by a comma."
gets.chomp.split(",").collect{ |s| s.to_i }
end
Looking at it, you might prefer a hash, keyed by book. Something like this:
book_sales = books_array.inject({}) do |hash, book|
puts "Please input weekly sales of #{books_array[0]} separated by a comma."
weekly_sales = gets.chomp.split(",").collect{ |s| s.to_i }
hash[book] = weekly_sales
end
This solution assumes that there will never be a duplicate book title. I figure that is pretty safe, yes?
input = "A list of words"
hash = {}
input.split(/\s+/).collect { |word| hash[word] = [] }
# Now do whatever with each entry
hash.each do |word,ary|
ary << ...
end