New to Ruby - pls help in translating this


#1

Hi,

I’m starting to use Ruby in one of my projects at work. I’m coming from
a
Perl background.
In my project I would need to parse a list of numbers (thousands of
them)
and then return the duplicates. In perl, I can do this:

Perl code

%hash = {};
while (<>)
{
chomp;
$hash{$_}++;
}

foreach my $key (sort keys %hash)
{
print “$key: $hash{$key}\n” if ($hash{$key} > 1);
}

I tried to translate this in Ruby, but could not find en equivalent of
$hash{$_}++, this is auto increment.
Can somebody tell me how this is to be done in Ruby? Or maybe the Ruby
way on how to attack this whole thing. Thanks.

Regards,
Sam


#2

On Dec 9, 2005, at 12:48 PM, Sam Dela C. wrote:

%hash = {};

I tried to translate this in Ruby, but could not find en equivalent of
$hash{$_}++, this is auto increment.

See if this gets you going:

seen = Hash.new(0)
ARGF.each_line { |line| seen[line.strip] += 1 }

seen.each { |key, value| puts key if value > 1 }

James Edward G. II


#3

use the following to initiate your hash:

h=Hash.new(0)

and this to increment on each key:

h[key] = h[key] + 1


#4

On Dec 9, 2005, at 1:48 PM, Sam Dela C. wrote:

%hash = {};

hash = Hash.new { |h, k| h[k] = 0 }

while gets
$.chomp!
hash[$
] += 1
end

I tried to translate this in Ruby, but could not find en equivalent of
$hash{$_}++, this is auto increment.

Ruby has no auto-increment since variables are more like labels on
objects than containers for objects and numbers are generally
immutable in ruby.
IOW:
x = 3
x++ in ruby would be like typing 3++ which doesn’t make sense really.


#5

On 12/9/05, Sam Dela C. removed_email_address@domain.invalid wrote:

Hi,

I’m starting to use Ruby in one of my projects at work. I’m coming from a
Perl background.
In my project I would need to parse a list of numbers (thousands of them)
and then return the duplicates. In perl, I can do this:

[elided perl goo]

I tried to translate this in Ruby, but could not find en equivalent of
$hash{$_}++, this is auto increment.
Can somebody tell me how this is to be done in Ruby?

translating from Perl to Ruby seems often to be a bad idea … a
common idea, but not necessarily a good one. I’d rather work
with a Ruby solution to a problem than a Rubification of a Perl
solution to a problem.

Or maybe the Ruby
way on how to attack this whole thing. Thanks.

I’m assuming that your list comes from a file (but you can change that
pretty easily in the code below), given that, how about something like:

seen_ary = Array.new

File.open(“nums”,“r”).each do |elem|
print elem if seen_ary.include?(elem)
seen_ary.push(elem)
end

(there are probably still better ways of doing this though)


#6

well, there is the succ method. and there’s a succ! on String, which
could
work in this case, I guess(?), since:

irb(main):023:0> a = “9”
=> “9”
irb(main):024:0> a.succ!
=> “10”


#7

variables are more like labels on objects than containers for objects

There is something very fundamental about what you are saying here but
I don’t quite understand. Could you elaborate on this with perhaps an
example?


#8

Or, something else to think about… shamelessly borrowed from this
mailing list a month or so ago…
Wrapped in lame ‘gets’ code to let you play with it at the command
line. I presume you’d actually do something cooler with STDIN or a
filename.

class Array
def dups
h, d = {}, []; each{|e| h[e] ? (d << h.delete(e)) : (h[e] = e)}; d
end
end
numbers = []
while n = STDIN.gets.chomp
break if n == ‘’
numbers << n
end
puts numbers.dups

I love reopening Array.

–Wilson.


#9

Hey,

after looking at your code (wich was a bit hard, since i don’t speak
perl) - i
came up with following solution, that doesn’t seem very ruby-esque but
works
well for me.
I’m sure someone brings the code down to one line, but i’m a bit too
lazy to
try that :slight_smile:

file = File.open(ARGV[0]).readlines
h = {}
file.each{|x| (h[x].nil?) ? (h[x] = 1) : (h[x] = h[x]+=1)}
h.each_pair{|k,v| puts “#{k.strip} appears #{v} times” if v >= 2}

Am Freitag, 9. Dezember 2005 19:48 schrieb Sam Dela C.:


#10

Quoting Sam Dela C. removed_email_address@domain.invalid:

%hash = {};

I tried to translate this in Ruby, but could not find en
equivalent of $hash{$_}++, this is auto increment.

It also autovivifies the hash element, but Ruby doesn’t have
autovivification.

Here’s a nearly literal translation to Ruby (the main difference is
that gets is like , not <>):

hash = {}
while gets
chomp
hash[$] ||= 0 # vivify
hash[$
] += 1 # increment
end

for key in hash.keys.sort
print “#{key}: #{hash[key]}\n” if hash[key] > 1
end

Here’s the same thing in a slightly more Ruby-ish style ($_ is
normally avoided in Ruby, even though it’s available):

hash = Hash.new( 0 )
$stdin.each do |line|
hash[line.chomp] += 1
end

hash.keys.sort.each do |key|
puts “#{key}: #{hash[key]}” if hash[key] > 1
end

Here, we create a hash whose default value for uninitialized
elements is 0, rather than nil (nil is like Perl’s undef). Note
that a default value you provide this way is used directly for
every element; it is not copied.

Note also that line.chomp is not the same thing as chomp $line in
Perl; line.chomp returns a new string rather than modifying the
existing one. The exact equivalent of Perl’s chomp $line would be
line.chomp!.

-mental


#11

I’ll go with:

seen = {}

ARGF.each do |elem|
print elem if seen.include? elem
seen[elem] = true
end

Thanks, this is how ruby should look like!

here is another one (i like it a bit more
functional style):

quantities = Hash.new{|h, k| h[k]=0}
ARGF.each{|l| quantities[l.chomp.to_i] += 1}
puts quantities.delete_if{|k, v| v <= 1}.keys

cheers

Simon


#12

On Dec 9, 2005, at 11:23 AM, pat eyler wrote:

[elided perl goo]

I tried to translate this in Ruby, but could not find en
equivalent of
$hash{$_}++, this is auto increment.
Can somebody tell me how this is to be done in Ruby?

translating from Perl to Ruby seems often to be a bad idea … a
common idea, but not necessarily a good one. I’d rather work
with a Ruby solution to a problem than a Rubification of a Perl
solution to a problem.

Ditto. I often find that I can make my code close to readable
English and find that a very good thing.

seen_ary.push(elem)
end

(there are probably still better ways of doing this though)

I’ll go with:

seen = {}

ARGF.each do |elem|
print elem if seen.include? elem
seen[elem] = true
end


Eric H. - removed_email_address@domain.invalid - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com


#13

On Dec 9, 2005, at 11:37 AM, Wilson B. wrote:

end
end

That is far too complicated and impossible to read. I think we
should be giving new people examples of how to make code clear and
expressive.

numbers = []
while n = STDIN.gets.chomp

$ echo -n ‘’ | ruby -e ‘p STDIN.gets’
nil

break if n == ‘’
numbers << n
end
puts numbers.dups

I love reopening Array.

I like clear, expressive code: [ruby-talk:169927]


Eric H. - removed_email_address@domain.invalid - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com


#14

On Dec 9, 2005, at 2:24 PM, JB Eriksson wrote:

well, there is the succ method. and there’s a succ! on String,
which could
work in this case, I guess(?), since:

irb(main):023:0> a = “9”
=> “9”
irb(main):024:0> a.succ!
=> “10”

Well, if it was a string. The problem is fixnums are immediate
values. ++ would therefore be an operation on the variable a, rather
than the object that a points at.


#15

On Dec 9, 2005, at 2:31 PM, Dan D. wrote:

variables are more like labels on objects than containers for objects

There is something very fundamental about what you are saying
here but I don’t quite understand. Could you elaborate on this with
perhaps an example?


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Well basically, all variables in ruby are references (or pointers,
whatever you want to call them), but they are actually even less
“clingy” than that.

maybe an example will help

x = “a string”
y = x # this doesn’t do something like x.copy nor is it even
equalivalent to typing y = “a string”
# it more like saying
# x =
# “a string”
# y =

y.upcase! #=> “A STRING”
x #=> “A STRING”

Just think of varibles as a way to refer to a memory address
If x and y “contain” anythjing it is a memory address and they both
have the same memory.

Basically they are pointers. Except when they aren’t. Fixnums for
instance are stored as values. As are symbols. I think I might have
over complicated this. Maybe someone else can explain it better.


#16

On Dec 9, 2005, at 2:53 PM, Sam Dela C. wrote:

Here’s what I decided on using (looks more like what I originally
posted
in perl):

hash = Hash.new(0)
File.open(ARGV[0],“r”).each do |line|

Replacing the above with:

ARGF.each do |line|

Is the same thing, but more powerful. You could feed it multiple
files at once, or use it in pipelined processing. Just FYI.

James Edward G. II


#17

Quoting Sam Dela C. removed_email_address@domain.invalid:

end
One caution here – if you want the file handle to be closed when
you are finished, you must do either:

stream = File.open(ARGV[0],“r”)
stream.each do |line|
hash[line.chomp] += 1
end
stream.close

or (this is often better because it will automatically close the
handle even if there’s an exception):

File.open(ARGV[0],“r”) do |stream|
stream.each do |line|
hash[line.chomp] += 1
end
end

-mental


#18

Yes, file handles must be closed. I learned that the hard way on one of
my projects before. Thanks again.
Sam

removed_email_address@domain.invalid
12/09/2005 01:02 PM

To
Sam Dela C./SVL/SC/PHILIPS@PHILIPS
cc

Subject
Re: new to Ruby - pls help in translating this
Classification

Quoting Sam Dela C. removed_email_address@domain.invalid:

end
One caution here – if you want the file handle to be closed when
you are finished, you must do either:

stream = File.open(ARGV[0],“r”)
stream.each do |line|
hash[line.chomp] += 1
end
stream.close

or (this is often better because it will automatically close the
handle even if there’s an exception):

File.open(ARGV[0],“r”) do |stream|
stream.each do |line|
hash[line.chomp] += 1
end
end

-mental


#19

Thank you all. I learned a little bit more ruby. And yes, I want to do
things the Ruby way, but I just can’t help to think perl still and then
translate to ruby. This is very similar to when I came to the U.S. and
all of a sudden I have to talk in English, I still think in my original
language(Tagalog) and then translate it in English and it doesn’t always
come up the way English speakers would say it. But I get the point
accross. But yes, going back to Ruby, I’d like to learn things the Ruby
way and so far I have good things to say about Ruby. One, it being so
readable, and second I think it is easier to learn especially the OOP
part
of it. In perl OOP is a big hurdle.

Here’s what I decided on using (looks more like what I originally posted
in perl):

hash = Hash.new(0)
File.open(ARGV[0],“r”).each do |line|
hash[line.chomp] += 1
end

hash.keys.sort.each do |key|
puts “#{key}: #{hash[key]}” if hash[key] > 1
end

Regards,
Sam Dela C.

Eric H. removed_email_address@domain.invalid
12/09/2005 11:39 AM
Please respond to
removed_email_address@domain.invalid

To
removed_email_address@domain.invalid (ruby-talk ML)
cc

Subject
Re: new to Ruby - pls help in translating this
Classification

On Dec 9, 2005, at 11:23 AM, pat eyler wrote:

[elided perl goo]

I tried to translate this in Ruby, but could not find en
equivalent of
$hash{$_}++, this is auto increment.
Can somebody tell me how this is to be done in Ruby?

translating from Perl to Ruby seems often to be a bad idea … a
common idea, but not necessarily a good one. I’d rather work
with a Ruby solution to a problem than a Rubification of a Perl
solution to a problem.

Ditto. I often find that I can make my code close to readable
English and find that a very good thing.

seen_ary.push(elem)
end

(there are probably still better ways of doing this though)

I’ll go with:

seen = {}

ARGF.each do |elem|
print elem if seen.include? elem
seen[elem] = true
end


Eric H. - removed_email_address@domain.invalid - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com


#20

On Dec 9, 2005, at 3:02 PM, removed_email_address@domain.invalid wrote:

hash.keys.sort.each do |key|
stream.close

or (this is often better because it will automatically close the
handle even if there’s an exception):

File.open(ARGV[0],“r”) do |stream|
stream.each do |line|
hash[line.chomp] += 1
end
end

Or:

File.foreach(ARGV.first) do |line|

end

James Edward G. II