An elegant way to modify all lines from file by using map() function?

ruby-talk
1

Hi all,

I'm new in ruby and I just have a question: in python when I want to
read all lines from file, do something with all of them and then use
them in my program I use map function + lambda function, sth like
that:

print map(lambda u: u.upper(), open("foo", "r").readlines())

but in your language I didn't find the way to create in one step array
of all lines from file, that could be used by map(). If I really want
to use map in this situation I have to use secondary array (called
arr) like in this snippet?

arr = Array.new
File.open('foo').each_line{ |l| arr.push l }
p arr.collect{ |l| l.upcase }

Please post a code-snippet, it's quite interesting to me :slight_smile:

2

puts File.readlines("foo").map {|l| l.upcase}

···

At 2010-01-21 05:17PM, "RobertGawron" wrote:

I'm new in ruby and I just have a question: in python when I want to
read all lines from file, do something with all of them and then use
them in my program I use map function + lambda function, sth like
that:

print map(lambda u: u.upper(), open("foo", "r").readlines())

--
Glenn Jackman
    Write a wise saying and your name will live forever. -- Anonymous

3

On 1.8.7+, you can use .lines to get an Enumerator:

p File.open('foo').lines.map {|l| l.upcase}

- Charlie

···

On Thu, Jan 21, 2010 at 4:20 PM, RobertGawron <mojwpisdao@gmail.com> wrote:

but in your language I didn't find the way to create in one step array
of all lines from file, that could be used by map(). If I really want
to use map in this situation I have to use secondary array (called
arr) like in this snippet?

arr = Array.new
File.open('foo').each_line{ |l| arr.push l }
p arr.collect{ |l| l.upcase }

4

Hi,

Hi all,

I'm new in ruby and I just have a question: in python when I want to
read all lines from file, do something with all of them and then use
them in my program I use map function + lambda function, sth like
that:

print map(lambda u: u.upper(), open("foo", "r").readlines())

but in your language I didn't find the way to create in one step array
of all lines from file, that could be used by map(). If I really want
to use map in this situation I have to use secondary array (called
arr) like in this snippet?

arr = Array.new
File.open('foo').each_line{ |l| arr.push l }
p arr.collect{ |l| l.upcase }

Please post a code-snippet, it's quite interesting to me :slight_smile:

Waow awesome how the order is in Python...

Let's take the natural order, welcome to Ruby !

puts File.read('foo').lines.map { |line| line.upcase }
That's in ruby 1.9
Notice lines is an Enumerator, that can be converted to an Array if needed
by #to_a

You got also IO.readlines

···

2010/1/21 RobertGawron <mojwpisdao@gmail.com>

5

Thanks

···

On Jan 21, 11:23 pm, Glenn Jackman <gle...@ncf.ca> wrote:

At 2010-01-21 05:17PM, "RobertGawron" wrote:

> I'm new in ruby and I just have a question: in python when I want to
> read all lines from file, do something with all of them and then use
> them in my program I use map function + lambda function, sth like
> that:

> print map(lambda u: u.upper(), open("foo", "r").readlines())

puts File.readlines("foo").map {|l| l.upcase}

--
Glenn Jackman
Write a wise saying and your name will live forever. -- Anonymous

6

Don't stop there! Take advantage of the Symbol#to_proc behavior:

puts File.read('foo').lines.map(&:upcase)

:wink:

-Rob

Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com

···

On Jan 21, 2010, at 5:40 PM, Benoit Daloze wrote:

Hi,

2010/1/21 RobertGawron <mojwpisdao@gmail.com>

Hi all,

I'm new in ruby and I just have a question: in python when I want to
read all lines from file, do something with all of them and then use
them in my program I use map function + lambda function, sth like
that:

print map(lambda u: u.upper(), open("foo", "r").readlines())

but in your language I didn't find the way to create in one step array
of all lines from file, that could be used by map(). If I really want
to use map in this situation I have to use secondary array (called
arr) like in this snippet?

arr = Array.new
File.open('foo').each_line{ |l| arr.push l }
p arr.collect{ |l| l.upcase }

Please post a code-snippet, it's quite interesting to me :slight_smile:

Waow awesome how the order is in Python...

Let's take the natural order, welcome to Ruby !

puts File.read('foo').lines.map { |line| line.upcase }
That's in ruby 1.9
Notice lines is an Enumerator, that can be converted to an Array if needed
by #to_a

You got also IO.readlines

7

This does not close the file handle properly.

I'd rather do something like this:

File.foreach('foo').map {|l| l.upcase}

File.foreach('foo').map(&:upcase)

These have the advantage over some of the presented solutions that
they do not create two large Arrays in memory but just one - the
mapped version.

Kind regards

robert

···

2010/1/21 Charles Oliver Nutter <headius@headius.com>:

On Thu, Jan 21, 2010 at 4:20 PM, RobertGawron <mojwpisdao@gmail.com> wrote:

but in your language I didn't find the way to create in one step array
of all lines from file, that could be used by map(). If I really want
to use map in this situation I have to use secondary array (called
arr) like in this snippet?

arr = Array.new
File.open('foo').each_line{ |l| arr.push l }
p arr.collect{ |l| l.upcase }

On 1.8.7+, you can use .lines to get an Enumerator:

p File.open('foo').lines.map {|l| l.upcase}

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

8

Thanks for all replies.