I have a model connected to a log, so I'm beginning to build ways to use that info with the model and pass it around elsewhere.
this method:
def read_log
counter = 1
f = File.open(self.log_file_path, 'r')
while (line = f.gets)
puts "#{counter}: #{line}"
counter = counter + 1
end
end
works, and dumps the log to the command line but ends with nil, so it reads it out to stdout but when calling that I get nothing. How can I read the contents into a more useful format? I need to read this into a controller variable for a template within rails on a webpage. It is basic, but something I haven't done yet.
contents = f.read
Now contents contains... the contents. Not sure what "useful" means in your context, but you can do things like split on newline to get each line.
You can also create an enumerator via f.lines, whether or not that's more useful, not sure.
Related
I am having trouble outputting the contents of my hash to a file. The program is one that manages a list of student records, including their StudentID, first name, last name, Major, and catalog year. Once the user is finished adding records, it is then added to the hash.
Everything in the program works perfectly, except when I try running the quit_program function, it doesn't save the contents in the file. Additionally, i am not getting any errors, any ideas?
could it potentially not be working because it is having trouble with converting the text in my hash, which is alphanumeric, into the text file?
def quit_program()
puts "Save Changes? y/n"
#changes = gets().chomp
if #changes=="y"
#fh=File.open(#file_name, 'w')
#this_string=""
#sDB.each do |key, store_account_data| #line 50
puts "#{key}: #{store_account_data.join(',')}"
end
end
#fh.puts(#this_string)
#fh.close()
end
You're not writing anything to the file. The string #this_string is empty. You should do
#sDB.each do |key, store_account_data|
#fh.puts "#{key}: #{store_account_data.join(',')}"
end
it doesn't save the contents in the file.
The following is NOT how you write to a file:
puts "#{key}: #{store_account_data.join(',')}"
That is how you write to your terminal/console window.
And this code:
#this_string=""
#fh.puts(#this_string)
writes a blank string to the file.
Here is how you write to a file:
class Student
def initialize(sDB, filename)
#sDB = sDB
#filename = filename
end
def save_changes()
puts "Save Changes? y/n"
user_answer = gets().chomp
if user_answer == "y"
File.open(#file_name, 'w') do |f|
#sDB.each do |key, store_account_data| #line 50
f.puts "#{key}: #{store_account_data.join(',')}"
end
end
end
end
could it potentially not be working because it is having trouble with
converting the text in my hash, which is alphanumeric, into the text
file?
No. Here is a concrete example you can try:
data = {
"John" => ['a', 123, 'b', 456],
"Sally" => ['c', 789, 'b', 0]
}
File.open('data.txt', 'w') do |f|
data.each do |name, data|
f.puts "#{name}: #{data.join(',')}"
end
end
$ ruby myprog.rb
$ cat data.txt
John: a,123,b,456
Sally: c,789,b,0
Also, ruby indenting is 2 spaces--not 0 spaces or 3 spaces, or anything else.
The answer is given in the error message: undefined local variable or method 'sDB'. (Which you have since removed from your question making the edited version next to impossible to answer.) Where and when is sDB defined in your program? You are evidently attempting to quit before initializing it.
In any case it is not a good thing to be accessing instance variables directly inside other methods. You should use accessor (getter and setter) methods instead. That would have probably prevented this situation from biting you in the first place.
def sdb
#sDB ||= Hash.new
end
def sdb=( key, value )
sdb
#sDB[ key ] = value
end
. . .
You are not properly writing to a file even if #sDB is defined. See Ruby - Printing a hash to txt file for an example.
Your question is missing essential input data, so there's no way to test our suggested changes.
Here's untested code I'd work from:
def quit_program
puts "Save Changes? y/n"
if gets.chomp.downcase == 'y'
File.write(
#file_name,
#s_db.map{ |k, v| "#{ k }: #{ v.join(',') }" }.join("\n")
)
end
end
Note:
#sDB isn't a proper variable name in Ruby. We use snake_case, not camelCase for variables and method names. ItsAMatterOfReadability. Follow the convention or suffer the wrath of your team members the first time you have a code review.
Don't add empty parenthesis to method names (quit_program()) or calls (gets()) unless it's essential to tell the difference between a variable and a method invocation. You should also never name a variable the same as a method because it'll confuse everyone working on the code, so that should never be a consideration.
Don't create a variable (#changes) you use once and throw away, unless what you're doing is so complex you need to break down the operation into smaller chunks. And, if you're doing that, it'd be a really good candidate for refactoring into separate methods, so again, just don't.
When comparing user-input to something you expect, fold the case of their input to match what you expect. (gets.chomp.downcase == 'y'). It really irritates users to enter "y" and fail because you insisted on "Y".
While you can use File.open to create or write to a file, there's less visual noise to use File.write. open is great when you need to use various options for the mode but for plain text write is sufficient.
The whole block used for writing looks like it can be cleaned up to a single map and join, which coerces the data into an array of strings then into a single string.
For an assignment, I'm using the Dir.glob method to read a series of famous speech files, and then perform some basic speech analytics on each one (number of words, number of sentences, etc). I'm able to read the files, but have not figured out how to read each file into a variable, so that I may operate on the variables later.
What I've got is:
Dir.glob('/students/~pathname/public_html/speeches/*.txt').each do |speech|
#code to process the speech.
lines = File.readlines(speech)
puts lines
end
This prints all the speeches out onto the page as one huge block of text. Can anyone offer some ideas as to why?
What I'd like to do, within that code block, is to read each file into a variable, and then perform operations on each variable such as:
Dir.glob('/students/~pathname/public_html/speeches/*.txt').each do |speech|
#code to process the speech.
lines = File.readlines(speech)
text = lines.join
line_count = lines.size
sentence_count = text.split(/\.|\?|!/).length
paragraph_count = text.split(/\n\n/).length
puts "#{line_count} lines"
puts "#{sentence_count} sentences"
puts "#{paragraph_count} paragraphs"
end
Any advice or insight would be hugely appreciated! Thanks!
Regarding your first question:
readLines converts the file into an array of Strings and what you then see is the behaviour of puts with an array of Strings as the argument.
Try puts lines.inspect if you would rather see the data as an array.
Also: Have a look at the Ruby console irb in case you have not done so already. It is very useful for trying out the kinds of things you are asking about.
Here's what wound up working:
speeches = []
Dir.glob('/PATH TO DIRECTORY/speeches/*.txt').each do |speech|
#code to process the speech.
f = File.readlines(speech)
speeches << f
end
def process_file(file_name)
# count the lines
line_count = file_name.size
return line_count
end
process_file(speeches[0])
I'm currently learning ruby and here what I'm trying to do:
A script which open a file, make a subsitution, then comparing every lines to each other to see if it exist many times.
So, I tried to work directly with the string, but I didn't find how to do it, so I put every line in an array, and comparing every row.
But I got a first problem.
Here is my code:
#!/usr/bin/env ruby
DOC = "test.txt"
FIND = /,,^M/
SEP = "\n"
#make substitution
puts File.read(DOC).gsub(FIND, SEP)
#open the file and put every line in an array
openFile = File.open(DOC, "r+")
fileArray = openFile.each { |line| line.split(SEP) }
#print fileArray #--> give the name of the object
#Cross the array to compare every items to every others
fileArray.each do |items|
items.chomp
fileArray.each do |items2|
items2.chomp
#Delete if the item already exist
if items = items2
fileArray.delete(items2)
end
end
end
#Save the result in a new file
File.open("test2.txt", "w") do |f|
f.puts fileArray
end
At the end, I only have the name of the array object "fileArray". I print the object after the split, and i've got the same, so I guess the problem is from here. Little help required (if you know how to do this without array, just with the line in the file, answer appreciate too).
Thanks !
EDIT:
So, here's my code now
#!/usr/bin/env ruby
DOC = "test.txt"
FIND = /,,^M/
SEP = "\n"
#make substitution
File.read(DOC).gsub(FIND, SEP)
unique_lines = File.readlines(DOC).uniq
#Save the result in a new file
File.open('test2.txt', 'w') { |f| f.puts(unique_lines) }
Can't figure out how to chomp this.
Deleting duplicate lines in a file:
no_duplicate_lines = File.readlines("filename").uniq
No need to write so much code :)
Modify your code like this:
f.puts fileArray.join("\n")
Alternate way:
unique_lines = File.readlines("filename").uniq
# puts(unique_lines.join("\n")) # Uncomment this line and see if the variable holds the result you want...
File.open('filename', 'w') {|f| f.puts(unique_lines.join("\n"))}
Just a couple of points about the original code:
fileArray = openFile.each { |line| line.split(SEP) }
sets fileArray to a File object, which I suspect wasn't your intention. File#each (the # notation is Ruby convention to describe a particular method on an object of the supplied class) executes your supplied block for each line (it's also available with a synonym: each_line), where a line is defined by default as your OS's end-line character(s).
If you were looking to build an array of lines, then you could just have written
fileArray = openFile.readlines
and if you wanted those lines to be chomped (often a good idea) then that could be achieved by something like
fileArray = openFile.readlines.collect { |line| line.chomp }
or even (since File mixes in Enumerable)
fileArray = openFile.collect { |line| line.chomp }
And one other tiny thing: Ruby tests for equality with ==, = is only for assignment, so
if items = items2
will set items to items2 (and will always evaluate as true)
Is there a good way to read, edit, and write files in place in Ruby?
In my online search I've found stuff suggesting to read it all into an array, modify said array, then write everything out. I feel like there should be a better solution, especially if I'm dealing with a very big file.
Something like:
myfile = File.open("path/to/file.txt", "r+")
myfile.each do |line|
myfile.replace_puts('blah') if line =~ /myregex/
end
myfile.close
Where replace_puts would write over the current line, rather than (over)writing the next line as it currently does because the pointer is at the end of the line (after the separator).
So then every line that matches /myregex/ will be replaced with 'blah'. Obviously what I have in mind is a bit more involved than that, as far as processing, and would be done in one line, but the idea is the same - I want to read a file line by line, and edit certain lines, and write out when I'm done.
Maybe there's a way to just say "rewind back to just after the last separator"? Or some way of using each_with_index and write via a line index number? I couldn't find anything of the sort, though.
The best solution I have so far is to read things line-wise, write them out to a new (temp) file line-wise (possibly edited), then overwrite the old file with the new temp file and delete. Again, I feel like there should be a better way - I don't think I should have to create a new 1gig file just to edit some lines in an existing 1GB file.
In general, there's no way to make arbitrary edits in the middle of a file. It's not a deficiency of Ruby. It's a limitation of the file system: Most file systems make it easy and efficient to grow or shrink the file at the end, but not at the beginning or in the middle. So you won't be able to rewrite a line in place unless its size stays the same.
There are two general models for modifying a bunch of lines. If the file is not too large, just read it all into memory, modify it, and write it back out. For example, adding "Kilroy was here" to the beginning of every line of a file:
path = '/tmp/foo'
lines = IO.readlines(path).map do |line|
'Kilroy was here ' + line
end
File.open(path, 'w') do |file|
file.puts lines
end
Although simple, this technique has a danger: If the program is interrupted while writing the file, you'll lose part or all of it. It also needs to use memory to hold the entire file. If either of these is a concern, then you may prefer the next technique.
You can, as you note, write to a temporary file. When done, rename the temporary file so that it replaces the input file:
require 'tempfile'
require 'fileutils'
path = '/tmp/foo'
temp_file = Tempfile.new('foo')
begin
File.open(path, 'r') do |file|
file.each_line do |line|
temp_file.puts 'Kilroy was here ' + line
end
end
temp_file.close
FileUtils.mv(temp_file.path, path)
ensure
temp_file.close
temp_file.unlink
end
Since the rename (FileUtils.mv) is atomic, the rewritten input file will pop into existence all at once. If the program is interrupted, either the file will have been rewritten, or it will not. There's no possibility of it being partially rewritten.
The ensure clause is not strictly necessary: The file will be deleted when the Tempfile instance is garbage collected. However, that could take a while. The ensure block makes sure that the tempfile gets cleaned up right away, without having to wait for it to be garbage collected.
If you want to overwrite a file line by line, you'll have to ensure the new line has the same length as the original line. If the new line is longer, part of it will be written over the next line. If the new line is shorter, the remainder of the old line just stays where it is.
The tempfile solution is really much safer. But if you're willing to take a risk:
File.open('test.txt', 'r+') do |f|
old_pos = 0
f.each do |line|
f.pos = old_pos # this is the 'rewind'
f.print line.gsub('2010', '2011')
old_pos = f.pos
end
end
If the line size does change, this is a possibility:
File.open('test.txt', 'r+') do |f|
out = ""
f.each do |line|
out << line.gsub(/myregex/, 'blah')
end
f.pos = 0
f.print out
f.truncate(f.pos)
end
Just in case you are using Rails or Facets, or you otherwise depend on Rails' ActiveSupport, you can use the atomic_write extension to File:
File.atomic_write('path/file') do |file|
file.write('your content')
end
Behind the scenes, this will create a temporary file which it will later move to the desired path, taking care of closing the file for you.
It further clones the file permissions of the existing file or, if there isn't one, of the current directory.
You can write in the middle of a file but you have to be carefull to keep the length of the string you overwrite the same otherwise you overwrite some of the following text. I give an example here using File.seek, IO::SEEK_CUR gives he current position of the file pointer, at the end of the line that is just read, the +1 is for the CR character at the end of the line.
look_for = "bbb"
replace_with = "xxxxx"
File.open(DATA, 'r+') do |file|
file.each_line do |line|
if (line[look_for])
file.seek(-(line.length + 1), IO::SEEK_CUR)
file.write line.gsub(look_for, replace_with)
end
end
end
__END__
aaabbb
bbbcccddd
dddeee
eee
After executed, at the end of the script you now have the following, not what you had in mind I assume.
aaaxxxxx
bcccddd
dddeee
eee
Taking that in consideration, the speed using this technique is much better than the classic 'read and write to a new file' method.
See these benchmarks on a file with music data of 1.7 GB big.
For the classic approach I used the technique of Wayne.
The benchmark is done withe the .bmbm method so that caching of the file doesn't play a very big deal. Tests are done with MRI Ruby 2.3.0 on Windows 7.
The strings were effectively replaced, I checked both methods.
require 'benchmark'
require 'tempfile'
require 'fileutils'
look_for = "Melissa Etheridge"
replace_with = "Malissa Etheridge"
very_big_file = 'D:\Documents\muziekinfo\all.txt'.gsub('\\','/')
def replace_with file_path, look_for, replace_with
File.open(file_path, 'r+') do |file|
file.each_line do |line|
if (line[look_for])
file.seek(-(line.length + 1), IO::SEEK_CUR)
file.write line.gsub(look_for, replace_with)
end
end
end
end
def replace_with_classic path, look_for, replace_with
temp_file = Tempfile.new('foo')
File.foreach(path) do |line|
if (line[look_for])
temp_file.write line.gsub(look_for, replace_with)
else
temp_file.write line
end
end
temp_file.close
FileUtils.mv(temp_file.path, path)
ensure
temp_file.close
temp_file.unlink
end
Benchmark.bmbm do |x|
x.report("adapt ") { 1.times {replace_with very_big_file, look_for, replace_with}}
x.report("restore ") { 1.times {replace_with very_big_file, replace_with, look_for}}
x.report("classic adapt ") { 1.times {replace_with_classic very_big_file, look_for, replace_with}}
x.report("classic restore") { 1.times {replace_with_classic very_big_file, replace_with, look_for}}
end
Which gave
Rehearsal ---------------------------------------------------
adapt 6.989000 0.811000 7.800000 ( 7.800598)
restore 7.192000 0.562000 7.754000 ( 7.774481)
classic adapt 14.320000 9.438000 23.758000 ( 32.507433)
classic restore 14.259000 9.469000 23.728000 ( 34.128093)
----------------------------------------- total: 63.040000sec
user system total real
adapt 7.114000 0.718000 7.832000 ( 8.639864)
restore 6.942000 0.858000 7.800000 ( 8.117839)
classic adapt 14.430000 9.485000 23.915000 ( 32.195298)
classic restore 14.695000 9.360000 24.055000 ( 33.709054)
So the in_file replacement was 4 times faster.
What I'm doing is this: have one file as input, another as output. I chose a random line in the input, put it in the output, and then delete it.
Now, I've iterated over the file and am on the line I want. I've copied it to the output file. Is there a way to delete it? I'm doing something like this:
for i in 0..number_of_lines_to_remove
line = rand(lines_in_file-2) + 1 #not removing the first line
counter = 0
IO.foreach("input.csv", "r") { |current_line|
if counter == line
File.open("output.csv", "a") { |output|
output.write(current_line)
}
end
counter += 1
}
end
So, I have current_line, but I'm not sure how to remove it from the source file.
Array.delete_at might do. Given an index, it removes the object at that index, returning the object.
input.csv:
one,1
two,2
three,3
Program:
#!/usr/bin/ruby1.8
lines = File.readlines('/tmp/input.csv')
File.open('/tmp/output.csv', 'a') do |file|
file.write(lines.delete_at(rand(lines.size)))
end
p lines # ["two,2\n", "three,3\n"]
output.csv:
one,1
Here is a randomline class. You create a new randomline object by passing it an input file name and an output file name. You can then call the deleterandom method on that object and pass it a number of lines to delete.
The data is stored internally in arrays as well as being put to file. Currently output is in append mode so if you use the same file it will just add to the end, you could change the a to a w if you wanted to start the file fresh each time.
class Randomline
attr_accessor :inputarray, :outputarray
def initialize(filein, fileout)
#filename = filein
#filein = File.open(filein,"r+")
#fileoutput = File.open(fileout,"a")
#inputarray = []
#outputarray = []
readin()
end
def readin()
#filein.each do |line|
#inputarray << line
end
end
def deleterandom(numtodelete)
numtodelete.times do |num|
random = rand(#inputarray.size)
#outputarray << inputarray[random]
#fileoutput.puts inputarray[random]
#inputarray.delete_at(random)
end
#filein = File.open(#filename,"w")
#inputarray.each do |line|
#filein.puts line
end
end
end
here is an example of it being used
a = Randomline.new("testin.csv","testout.csv")
a.deleterandom(3)
You have to re-write the source-file after removing a line otherwise the modifications won't stick as they're performed on a copy of the data.
Keep in mind that any operation which modifies a file in-place runs the risk of truncating the file if there's an error of any sort and the operation cannot complete.
It would be safer to use some kind of simple database for this kind of thing as libraries like SQLite and BDB have methods for ensuring data integrity, but if that's not an option, you just need to be careful when writing the new input file.