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comp.lang.ruby

output of a method to file?

Zoe Phoenix

4/8/2008 11:33:00 PM

Can anybody tell me how to take the output of a method and save it to a
file?

I have an array and I've created a method to take the strings I put into
the array and insert them into a place in a sentence. How do I execute
the method and save the output to a file? I just started with Ruby a
few days ago and I can have it save a file, but the file it saves is
empty.

Help, please?
--
Posted via http://www.ruby-....
14 Answers

Phillip Gawlowski

4/8/2008 11:53:00 PM

0

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Zoe Phoenix wrote:
| Can anybody tell me how to take the output of a method and save it to a
| file?
|
| I have an array and I've created a method to take the strings I put into
| the array and insert them into a place in a sentence. How do I execute
| the method and save the output to a file? I just started with Ruby a
| few days ago and I can have it save a file, but the file it saves is
| empty.
|
| Help, please?

Sure:
irb(main):003:0> to_file = [1,2,3,4,5]
=> [1, 2, 3, 4, 5]
irb(main):004:0> File.open("a_file.txt","w") do |f|
irb(main):005:1* f.write to_file
irb(main):006:1> end
=> 5
irb(main):007:0> exit

C:\temp>cat a_file.txt
12345

Let's walk a bit through the code:
to_file is your average Array.

The File class allows you to interact with files (most commonly, reading
and writing).

Fil.open("a_file.txt","w") opens a file called "a_file.txt" in write
mode (the "w"). It's important to tell Ruby the mode you want to use.
"r" is the mode to read files, "a" is the mode to append to a file, and
Windows has the mode "b" to handle binary files.
You can find a quick reference for that here:
http://www.zenspider.com/Languages/Ruby/QuickR...

The |f| is a bloack variable. I use that in the next line, to actually
write to the file:
f.write to_file This writes the content of the Array to a file. Note
that the Array is dumped similar to Array#join "". You'll have to add
line breaks somehow, if you want lines.

Anyway: This step in the block writes to the file.

end closes the block, and with that, Ruby takes care of closing the
file, too, so that you don't have to.

I hope that helps. (I have to look it up myself, more often than I would
like).

- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan

~ YAAH! DEATH TO OATMEAL!
-- Calvin
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Zoe Phoenix

4/9/2008 12:11:00 AM

0

Maybe it would help if I posted the code, I'm not sure I understand...
For example..:


def cityList
c_list = ['Boston', 'Nashville', 'San Francisco', 'Houston', 'Portland',
'Atlanta', 'Chicago', 'Indianapolis', 'Charleston']

bar = '|| '


puts bar + c_list[0..2].join(' pets || ') + (' pets ||')

puts bar + c_list[3..5].join(' pets || ') + (' pets ||')

puts bar + c_list[6..8].join(' pets || ') + (' pets ||')

end

cityList


puts 'File completed. Save as..?'
save_as = gets.chomp



File::open('c:\rubyfiles\citylist-' + save_as + '.txt', 'w') do |f|


***********

I need it to take the output of that method that I created and write it
to a file... I'm not sure I understand how to do that with the example
you gave. Since I know the code that I had after "File::open", etc. was
wrong, I just left it out.

It would also be nice if I could have the method cycle through 3 items
in the array, then write 3 to a new line, the continue in increments of
3 until it reaches the end of the array. But, I'm not sure if I should
write another topic to ask that or if someone will answer that here.
Thanks for the help so far, though... I'm pretty new at this.
--
Posted via http://www.ruby-....

Phillip Gawlowski

4/9/2008 12:37:00 AM

0

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Zoe Phoenix wrote:
| Maybe it would help if I posted the code, I'm not sure I understand...
| For example..:
|
|
| def cityList
| c_list = ['Boston', 'Nashville', 'San Francisco', 'Houston', 'Portland',
| 'Atlanta', 'Chicago', 'Indianapolis', 'Charleston']
|
| bar = '|| '
|
|
| puts bar + c_list[0..2].join(' pets || ') + (' pets ||')
|
| puts bar + c_list[3..5].join(' pets || ') + (' pets ||')
|
| puts bar + c_list[6..8].join(' pets || ') + (' pets ||')
|
| end
|
| cityList
|
|
| puts 'File completed. Save as..?'
| save_as = gets.chomp
|
|
|
| File::open('c:\rubyfiles\citylist-' + save_as + '.txt', 'w') do |f|
|
|
| ***********
|
| I need it to take the output of that method that I created and write it
| to a file... I'm not sure I understand how to do that with the example
| you gave. Since I know the code that I had after "File::open", etc. was
| wrong, I just left it out.

If it is allowed, I'll add some Ruby idioms (you'll find these often,
and will find them useful, I hope).

I saved your file as "saving.rb", and it now produces the following:

File completed. Save as..?
temp #that's the name I saved the file as

C:\temp>less c:\rubyfiles\citylist-temp.txt # This is how the file looks.
|| Boston pets || Nashville pets || San Francisco pets ||
|| Houston pets || Portland pets || Atlanta pets ||
|| Chicago pets || Indianapolis pets || Charleston pets ||

This is the reworked script:

def cityList
~ c_list = [
~ 'Boston',
~ 'Nashville',
~ 'San Francisco',
~ 'Houston',
~ 'Portland',
~ 'Atlanta',
~ 'Chicago',
~ 'Indianapolis',
~ 'Charleston'
~ ] # I just changed that for readability.

~ bar = '|| ' # I left this, too.

~ temp_array = [] #This is a temporary array,
#I use to store the results.
~ temp_array.push bar + c_list[0..2].join(' pets || ') + (' pets ||') +
"\n" # This pushes the result of into the Array. It gets stored at the
first index of the Array. You could access it via temp_array[0].

~ temp_array.push bar + c_list[3..5].join(' pets || ') + (' pets ||') +
"\n" #This does something similar, except that it is stored at the next
Array index, temp_array[1]

~ temp_array.push bar + c_list[6..8].join(' pets || ') + (' pets ||') +
"\n" # See above, except this time it is temp_array[2]. Notice that I
added "\n" to your code. This adds a new line. Just delete it, if you
don't want the whole output on a new line, or just leave the last one,
if every iteration shall be on a new line.

end

puts 'File completed. Save as..?'
save_as = gets.chomp

File.open("c:/rubyfiles/citylist-#{save_as}.txt","w") do |f| # Here, I
used string-interpolation, which only works with the double quotes (").
~ f.write cityList #This is a bit complex. f.write takes the result of
cityList, and writes it to a file. In Ruby, every method returns its
last action, so to speak. In this case, it is the Array with all three
lines. Also notice, that you don't have to use File::open, but that
should work, too.
end #ending the block again, and closing the file.

I hope that helps (In case it's not really readable, just copy and paste
the code into your favorite editor).


| It would also be nice if I could have the method cycle through 3 items
| in the array, then write 3 to a new line, the continue in increments of
| 3 until it reaches the end of the array. But, I'm not sure if I should
| write another topic to ask that or if someone will answer that here.

Let me repeat, to see if I got that correctly:
You want to do cityList three times, and write all of these iterations
into 3 seperate files?

In that case, you could just wrap the File.open[..] part into a loop.
Like 3.times do
File.open[...]
end

| Thanks for the help so far, though... I'm pretty new at this.

We all were, at one time. :)

I hope I can help you out.

In case you haven't found it: Chris Pine's Learn to Program helped me a
lot: pine.fm/LearnToProgram/

And _why's Piognant Guide to Ruby is good, too (although a bit..
strange): http://poignantguide...

- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan

~ There's never enough time to do all the nothing you want.
-- Calvin
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Zoe Phoenix

4/9/2008 1:03:00 AM

0

hm, let me re-phrase... I only have 9 items in that array, right? How
do I make the program continue through the array no matter how many
items are in it without having to go and edit the array that comes after
c_list?

~~temp_array.push c_list[0..2].join(' pets || ') + (' pets ||') +
"\n"

Like, say I added 3 more cities to the end of c_list, but I don't want
to have to add

~~temp_array.push c_list[9..11].join(' pets || ') + (' pets ||') +
"\n"


to the program. How can I make it cycle through the whole array without
having to edit c_list[number..number]? Is there a way to automate that,
so I only have to add cities to c_list without having to add more code?


And thanks, I've already found Mr. Pine's Learn To Program site and the
Poignant Guide.. :-) They've been a big help. I've tried to learn other
programming languages, but Ruby's been the easiest for me to understand.
--
Posted via http://www.ruby-....

Phillip Gawlowski

4/9/2008 1:13:00 AM

0

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Zoe Phoenix wrote:
| hm, let me re-phrase... I only have 9 items in that array, right? How
| do I make the program continue through the array no matter how many
| items are in it without having to go and edit the array that comes after
| c_list?

Oh, indeed you can.Array provides the #each and #each_with_index methods:

irb(main):001:0> array = [1,2,3,4,5]
=> [1, 2, 3, 4, 5]
irb(main):002:0> array.each{|a| puts a}
1
2
3
4
5
=> [1, 2, 3, 4, 5]

The above is Array#each. It allows you to operate on each element of
your array.


irb(main):003:0> array.each_with_index{|a,b| puts a;puts b}
1
0
2
1
3
2
4
3
5
4
=> [1, 2, 3, 4, 5]

Here, you get the current index, too (that is the second variable, I've
called b). This, of course, works with Strings also (like your city names).

Together with the % (modulo) operator, you can test if the index can be
divided by 3 without a remainder, so that you can add a new line after
the third element.

If that doesn't help you write your own code, I'll be happy to provide
an annotated example again.

- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan

~ - You know you've been hacking too long when...
...after days with YACC, you start to parse your conversations.
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Zoe Phoenix

4/9/2008 1:53:00 AM

0

I think I understand what you're saying, but I'm not quite sure how to
apply it...
--
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Phillip Gawlowski

4/9/2008 2:33:00 AM

0

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Zoe Phoenix wrote:
| I think I understand what you're saying, but I'm not quite sure how to
| apply it...

Let me show you an example:

irb(main):001:0> array = ["a","b","c","d","e"]
=> ["a", "b", "c", "d", "e"]
irb(main):002:0> array.each_with_index do |item, index|
irb(main):003:1* puts item if index % 3 == 0
irb(main):004:1> end
a
d
=> ["a", "b", "c", "d", "e"]

In this example, only the elements at an index that can be divided by 3
without a problem are printed. You can achieve a similar effect with a
counter, for example.

(My idea to use modulo was a bit off, sorry about that).

Translated to your problem:
saving.rb:

c_list = [
~ 'Boston',
~ 'Nashville',
~ 'San Francisco',
~ 'Houston',
~ 'Portland',
~ 'Atlanta',
~ 'Chicago',
~ 'Indianapolis',
~ 'Charleston'
~ ]

counter = 1
temp_array = []
c_list.each_with_index do |item,index|
~ temp_array.push "|| " if index % 3 == 0
~ temp_array.push "#{item} "
~ temp_array.push "pets ||"
~ temp_array.push "\n" if counter % 3 == 0
~ counter +=1
end
puts 'File completed. Save as..?'
save_as = gets.chomp


File.open("c:/rubyfiles/citylist-#{save_as}.txt","w") do |f|
~ f.write temp_array
end

What am I doing here (this is a very naive implementation, nothing
fancy, but it does what it is supposed to do)?

First, I create the array of cities (you can get fancy later on, and
read it from a file, too).

Then, I create a counter to help me later on, as well as an empty array.

After that, I iterate over the c_list array with the help of the
each_with_index method.

Now the fun starts:


temp_array.push "|| " if index % 3 == 0

This only gets done, in the case that I can divide the index by 3
without a remainder. This works with 0, so I get the "|| " part.


temp_array.push "#{item} "

This uses Ruby's String interpolation to create, for example, "Boston ".
String interpolation allows you to execute Ruby code within Strings,
roughly speaking. You can test that by doing puts "#{Time.now}" in irb,
for example.


temp_array.push "\n" if counter % 3 == 0

This pushes the newline character into the array for file output, in the
case that the counter variable I introduced earlier can be divided by 3
without a remainder.

This should give you at least a starting point, in case I missed what
you wanted.

File block you already know. :)

HTH,
- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan

~ - You know you've been hacking too long when...
...you begin to think in nested IF-THEN-ELSE clauses that would make a
bureaucrat get lost.
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Zoe Phoenix

4/9/2008 3:42:00 AM

0

hmm, I see what you're doing there...

I still can't seem to get the file block to actually write the output of
the method to a file. The file it writes still comes up empty...
--
Posted via http://www.ruby-....

Phillip Gawlowski

4/9/2008 3:46:00 AM

0

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Zoe Phoenix wrote:
| hmm, I see what you're doing there...
|
| I still can't seem to get the file block to actually write the output of
| the method to a file. The file it writes still comes up empty...

Are you explicitly calling the #write method? puts doesn't work (I fall
for that trap 9 times out of 10), unfortunately.

And are you opening the file in write / append mode?

Are you getting any errors from Ruby?

- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan

Each module should do one thing well.
~ - The Elements of Programming Style (Kernighan & Plaugher)
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Zoe Phoenix

4/9/2008 6:18:00 AM

0

def cityList
c_list = [
'Boston',
'Nashville',
'San Francisco',
'Houston',
'Portland',
'Atlanta',
'Chicago',
'Indianapolis',
'Charleston'
]

bar = '|| '

temp_array = []

temp_array.push puts bar + c_list[0..2].join(' pets || ') + (' pets
||'+'/n')

temp_array.push puts bar + c_list[3..5].join(' pets || ') + (' pets
||'+'/n')

temp_array.push puts bar + c_list[6..8].join(' pets || ') + (' pets
||'+'/n')

end



puts 'File completed. Save as..?'
save_as = gets.chomp



File::open("c:\rubyfiles\citylist-#{save_as}.txt", 'w') do |f|
f.write cityList

end

********

This is the error it gives me...:

directory\rubyprograms\cities.rb:33:in 'initialize':
ubyfiles tylist-city1.txt (Errno::EINVAL)
from directory\rubyprograms\cities.rb:33:in
'open'
from directory\rubyprograms\cities.rb:33

********


There's something wrong with the code, I know, but I'm not sure what.
--
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