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comp.lang.ruby

Looking for more Ruby-like way to create an array

Steve Nicholson

10/7/2008 9:34:00 PM

I'm creating an array that is the result of the members of another array
each multiplied by 100. Here's what I have:

converted_array = []
original_array.each {|line| converted_array << line.to_f * 100}

This works, but I'm wondering if there is a more idiomatically "Ruby"
way of doing it.
--
Posted via http://www.ruby-....
8 Answers

Tim Hunter

10/7/2008 9:40:00 PM

0

Steve Nicholson wrote:
> I'm creating an array that is the result of the members of another array
> each multiplied by 100. Here's what I have:
>
> converted_array = []
> original_array.each {|line| converted_array << line.to_f * 100}
>
> This works, but I'm wondering if there is a more idiomatically "Ruby"
> way of doing it.

Try map

converted_array = orginal_array.map {|line| line.to_f * 100 }

--
RMagick: http://rmagick.ruby...

Rimantas Liubertas

10/7/2008 9:43:00 PM

0

2008/10/8 Steve Nicholson <ssteve@mac.com>:
> I'm creating an array that is the result of the members of another array
> each multiplied by 100. Here's what I have:
>
> converted_array = []
> original_array.each {|line| converted_array << line.to_f * 100}
>
> This works, but I'm wondering if there is a more idiomatically "Ruby"
> way of doing it.

converted_array = original_array.map{|item| item.to_f * 100}

Regards,
Rimantas
--
http://rim...

Steve Nicholson

10/7/2008 9:49:00 PM

0

Tim Hunter wrote:

> Try map
>
> converted_array = orginal_array.map {|line| line.to_f * 100 }

Thanks, Tim, Rimantas, and Dan for the unanimous advice. I will study up
on map.
--
Posted via http://www.ruby-....

William James

10/7/2008 11:02:00 PM

0

On Oct 7, 4:33 pm, Steve Nicholson <sst...@mac.com> wrote:
> I'm creating an array that is the result of the members of another array
> each multiplied by 100. Here's what I have:
>
>   converted_array = []
>   original_array.each {|line| converted_array << line.to_f * 100}
>
> This works, but I'm wondering if there is a more idiomatically "Ruby"
> way of doing it.
> --
> Posted viahttp://www.ruby-....

irb(main):001:0> a = 2,3,5,8
=> [2, 3, 5, 8]
irb(main):002:0> a.map!{|n| n*10 }
=> [20, 30, 50, 80]
irb(main):003:0> a
=> [20, 30, 50, 80]

Bilyk, Alex

10/8/2008 1:32:00 AM

0

converted_array =3D original_array.inject([]) {|a, line| a << (line.to_f * =
100)}

-----Original Message-----
From: David A. Black [mailto:dblack@rubypal.com]
Sent: Tuesday, October 07, 2008 6:19 PM
To: ruby-talk ML
Subject: Re: Looking for more Ruby-like way to create an array

Hi --

On Wed, 8 Oct 2008, William James wrote:

> On Oct 7, 4:33 pm, Steve Nicholson <sst...@mac.com> wrote:
>> I'm creating an array that is the result of the members of another
>> array each multiplied by 100. Here's what I have:
>>
>> converted_array =3D []
>> original_array.each {|line| converted_array << line.to_f * 100}
>>
>> This works, but I'm wondering if there is a more idiomatically "Ruby"
>> way of doing it.
>> --
>> Posted viahttp://www.ruby-....
>
> irb(main):001:0> a =3D 2,3,5,8
> =3D> [2, 3, 5, 8]
> irb(main):002:0> a.map!{|n| n*10 }
> =3D> [20, 30, 50, 80]
> irb(main):003:0> a
> =3D> [20, 30, 50, 80]

That's a little different, since it leaves you without the original array (=
which may in fact be OK, but is an important difference).


David

--
Rails training from David A. Black and Ruby Power and Light:
Intro to Ruby on Rails January 12-15 Fort Lauderdale, FL
Advancing with Rails January 19-22 Fort Lauderdale, FL *
* Co-taught with Patrick Ewing!
See http://www.r... for details and updates!

David A. Black

10/8/2008 1:37:00 AM

0

Hi --

On Wed, 8 Oct 2008, Bilyk, Alex wrote:

> converted_array = original_array.inject([]) {|a, line| a << (line.to_f * 100)}

I'd definitely favor map over inject for this. It's much more
straightforward for this particular operation.


David

--
Rails training from David A. Black and Ruby Power and Light:
Intro to Ruby on Rails January 12-15 Fort Lauderdale, FL
Advancing with Rails January 19-22 Fort Lauderdale, FL *
* Co-taught with Patrick Ewing!
See http://www.r... for details and updates!

Joshua Abbott

10/8/2008 4:44:00 AM

0

I agree with David. I did a simple benchmarking test and you can already
see a difference with an array of ten integers:

irb(main):001:0> require 'benchmark'
=> true
irb(main):002:0> a = [1,2,3,4,5,6,7,8,9,10]
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
irb(main):003:0> Benchmark.bm do |b|
irb(main):004:1* b.report { new_array = a.inject([]) { |array,item|
array << item * 100 } }
irb(main):005:1> end
user system total real
0.000000 0.000000 0.000000 ( 0.000035)
=> true
irb(main):006:0> Benchmark.bm do |b|
irb(main):007:1* b.report { new_array = a.map { |item| item * 100 }
}
irb(main):008:1> end
user system total real
0.000000 0.000000 0.000000 ( 0.000022)
=> true
irb(main):009:0>

But if you up the ante (because how often is it that we deal with an
array of only ten elements?) you get something more like this:

irb(main):009:0> a = (0..250).map
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54,
55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72,
73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90,
91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106,
107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120,
121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134,
135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148,
149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162,
163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176,
177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190,
191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204,
205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218,
219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232,
233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246,
247, 248, 249, 250]
irb(main):010:0> Benchmark.bm do |b|
irb(main):011:1* b.report { new_array = a.inject([]) { |array,item|
array << item * 100 } }
irb(main):012:1> end
user system total real
0.000000 0.000000 0.000000 ( 0.000442)
=> true
irb(main):013:0> Benchmark.bm do |b|
irb(main):014:1* b.report { new_array = a.map { |item| item * 100 }
}
irb(main):015:1> end
user system total real
0.000000 0.000000 0.000000 ( 0.000165)
=> true
irb(main):016:0>

So you can see there's some substantial difference with map. Not to
mention, "map" just looks cleaner and creates an array by default (where
inject can do many different things).

You can get more background on why inject takes longer than map by
reading the documentation:

Map: http://ruby-doc.org/core/classes/Array.ht...
Inject: http://ruby-doc.org/core/classes/Enumerable.ht...

-- Josh
http://iammr...

David A. Black wrote:
> Hi --
>
> On Wed, 8 Oct 2008, Bilyk, Alex wrote:
>
>> converted_array = original_array.inject([]) {|a, line| a << (line.to_f * 100)}
>
> I'd definitely favor map over inject for this. It's much more
> straightforward for this particular operation.
>
>
> David

--
Posted via http://www.ruby-....

Robert Klemme

10/8/2008 12:37:00 PM

0

2008/10/8 David A. Black <dblack@rubypal.com>:
> On Wed, 8 Oct 2008, Bilyk, Alex wrote:
>
>> converted_array = original_array.inject([]) {|a, line| a << (line.to_f *
>> 100)}
>
> I'd definitely favor map over inject for this. It's much more
> straightforward for this particular operation.

Absolutely agree!

robert

--
remember.guy do |as, often| as.you_can - without end