Variable + string to specify variable

rubyonrails-talk
#1

Hi,

Novice question:

I need to assign an item id to one of 3 arrays randomly but can't figure
out how to specify the correct array by combining "arr" and the randomly
generated number...

id = "100"
x = rand(1..3)

arr1 = Array.new
arr2 = Array.new
arr3 = Array.new

selected_array = "#{'arr' + x}" *** Not sure how to do this ****

selected_array.push(id)

Thanks in advance,

Dave Castellano

#2

While you could append the name and eval, that's not really a clean approach. Just use an array of arrays. Or if else...

#3

To expand on what Scott is saying here is some code that gives an example of what he is referring to.

id = 100
x = rand(1…3)
arrays = [Array.new, Array.new, Array.new]
selected_array = arrays[x]
selected_array.push(id)

``

#4

To expand on what Scott is saying here is some code that gives an example of what he is referring to.

id = 100 x = rand(1..3) arrays = [Array.new, Array.new, Array.new] selected_array = arrays[x] selected_array.push(id)

And to make it a bit more flexible, you could do:

arrays = [ Array.new, Array.new, Array.new ]

x = rand(arrays.size)

arrays[x].push(id)

or even:

arrays = [ Array.new, Array.new, Array.new ]

arrays.sample.push(id)

http://www.ruby-doc.org/core-2.1.2/Array.html#method-i-sample

-Rob

#5

I knew there would be a nice simpler Ruby way. I love the second solution, Rob. Below is the updated example.

#6

One tiny note, this is purely a matter of style & taste, spelling it out vs concision, but I thought it might be good for your learning to understand that you could also use:

arrays = [[], [], []]

And, if you wanted a set of arrays that you access by string instead of int:

arrays = {'one' => [], 'two' => [], 'three' => []}
arrays['one'].push(42)
puts arrays['one'][0]

#7

You can simplify the arrays construction, too: (with slight reformatting of the arrays output)

irb2.1.1> arrays = Array.new(3) { Array.new }

#2.1.1 => [[], [], []]

irb2.1.1> 100.times {|id| arrays.sample.push(id) }

#2.1.1 => 100

irb2.1.1> arrays

#2.1.1 => [[0, 2, 6, 8, 9, 11, 14, 16, 17, 18, 22,

        24, 29, 31, 37, 42, 47, 49, 53, 54, 57, 

        58, 60, 68, 69, 73, 75, 79, 80, 81, 83, 

        88, 91, 94, 95, 96], 

       [1, 3, 12, 13, 20, 25, 26, 28, 33, 34,

        38, 39, 43, 44, 48, 50, 52, 59, 63, 65,

        70, 72, 74, 77, 78, 82, 86, 87, 89, 97],

       [4, 5, 7, 10, 15, 19, 21, 23, 27, 30, 

        32, 35, 36, 40, 41, 45, 46, 51, 55, 56,

        61, 62, 64, 66, 67, 71, 76, 84, 85, 90,

        92, 93, 98, 99]]

irb2.1.1> arrays.map(&:size)

#2.1.1 => [36, 30, 34]